Manufacturing method of semiconductor substrate and method and apparatus for inspecting defects of patterns of an object to be inspected

ABSTRACT

A pattern detection method and apparatus thereof for inspecting with high resolution a micro fine defect of a pattern on an inspected object and a semiconductor substrate manufacturing method and system for manufacturing semiconductor substrates such as semiconductor wafers with a high yield. A micro fine pattern on the inspected object is inspected by irradiating an annular-looped illumination through an objective lens onto a wafer mounted on a stage, the wafer having micro fine patterns thereon. The illumination light may be circularly or elliptically polarized and controlled according to an image detected on the pupil of the objective lens and image signals are obtained by detecting a reflected light from the wafer. The image signals are compared with reference image signals and a part of the pattern showing inconsistency is detected as a defect so that simultaneously, a micro fine defect or defects on the micro fine pattern are detected with high resolution. Further, process conditions of a manufacturing line are controlled by analyzing a cause of defect and a factor of defect which occurs on the pattern.

This application is a continuation of application Ser. No. 08/539,886filed Oct. 6, 1995, now U.S. Pat. No. 5,774,222.

FIELD OF THE INVENTION

The present invention relates to a manufacturing method of asemiconductor substrate such as a semiconductor wafer, a TFT (Thin FilmTransistor) liquid crystal substrate, a thin film multi-layer substrateand a printed board, which have respectively micro fine circuit patternsor wiring patterns, at a high yield rate, a method and apparatus formeasuring highly precise dimensions of patterns to be inspected, whichcomprises micro fine circuit patterns or wiring patterns formed on theobject to be inspected such as the semiconductor wafer, the TFT liquidcrystal substrate, the thin film multi-layer substrate and the printedboard and inspecting the patterns on the object to be inspected, amethod and apparatus for detecting micro fine defects of the patterns onthe object to be inspected, and a microscope to be used in theaforementioned detection method.

BACKGROUND OF THE INVENTION

Recently, the patterns to be inspected, each comprising circuit patternsor wiring patterns formed on, for example, the semiconductor wafer, theTFT liquid crystal substrate, the thin film multi-layer substrate andthe printed board have been adapted to be further micro-structured inresponse to the needs for high density integration. Since the circuitpatterns or the wiring patterns are further micro-structured along withhigh density integration, a defect which should be detected becomessmaller or finer. Detection of such micro fine defects has been anextremely important subject in determination of an integrity of thecircuit patterns or the wiring patterns in manufacturing of the circuitpatterns or the wiring patterns.

However, the above-described micro structure has been further advancedand detection of micro fine defects of the patterns to be inspected suchas the circuit patterns or the wiring patterns has reached the limit ofresolution of the imaging optical system, and therefore essentialimprovement of the resolution has been demanded.

A prior art apparatus for essentially improving the resolution isdisclosed in Japanese Patent Laid-Open No. Hei 5-160002. In thisdocument, there is disclosed a pattern inspection apparatus whichcomprises an illumination arrangement for providing an annular-loopeddiffusion illumination formed with arrays of a plurality of virtual spotlight sources for micro fine circuit patterns which is formed on a mask,through light source space filters, a light receiving arrangement havingan optical pupil which sufficiently introduces a diffraction light fromthe micro fine pattern, which passes through or reflected from a maskwhich is almost uniformly diffusion-illuminated by the illuminationarrangement and has imaging space filters for shutting off at least partof 0th order diffraction light or low order diffraction light of thisintroduced light, to obtain image signals by receiving the circuitpattern imaged through the optical pupil, and a comparison arrangementfor comparing the image signals obtained by the light receivingarrangement with mask pattern data or wafer pattern data or data from atransfer simulator to inspect the pattern. In this document, there isalso disclosed a method for controlling a shape of a light source spacefilter and an imaging space filter in accordance with the pattern shapedata.

However, there has been a problem that, though, in the above-describedprior art with respect to detection of a defect of the micro finepattern. That is, although a defect of the micro fine pattern isdetected by applying the annular-looped diffusion illumination to themicro fine pattern on the object to be inspected and sufficientlyintroducing the diffraction light from the micro fine pattern into theopening (pupil) of the objective lens to obtain high resolution imagesignals, full consideration has not been taken for the point that amicro fine defect should be detected with high reliability in responseto various micro fine patterns existing on the object to be inspected.

Further, full consideration has also not been given for manufacturingsemiconductor substrates having micro fine patterns such as asemiconductor wafer, a TFT liquid crystal substrate, a thin filmmulti-layer substrate and a printed board with reduced defects and highyield rate.

SUMMARY OP THE INVENTION

An object of the present invention is to solve the above problems of theprior art and to provide a method for manufacturing semiconductorsubstrates which is adapted to manufacture semiconductor substrates suchas, for example, a semiconductor wafer, a TFT liquid crystal substrate,a thin film multi-layer substrate and a printed board, each having microfine patterns, in a high yield rate.

Another object of the present invention is to provide a patterndetection method for detecting a pattern on an object to be inspectedand an apparatus thereof (microscope system) which are adapted to detecta defect of a micro fine pattern with high reliability in response tovarious micro fine patterns provided on objects to be inspected such asa semiconductor wafer, a TFT liquid crystal substrate, a thin filmmulti-layer substrate, and a printed board.

Another object of the present invention is to provide a method and anapparatus for inspecting a defect of a pattern on the object to beinspected which are adapted to inspect a micro fine defect of a microfine pattern with high reliability in response to various micro finepatterns provided on objects to be inspected such as a semiconductorwafer, a TFT liquid crystal substrate, a thin film multi-layersubstrate, and a printed board.

To achieve the above objects, a semiconductor substrate manufacturingmethod for manufacturing semiconductor substrates each having patternsformed by a manufacturing line comprising various process units,according to the present invention comprises: a history data or database build-up step for building up history data or data base which showsa relation of causes and effects by accumulating in advance the historydata or data base showing the relation of defect information of apattern which appears on the semiconductor substrate and a cause ofdefect or a factor of defect which causes a defect of the pattern in themanufacturing line; a defect inspection step for detecting the defectinformation of the pattern by comparing image signals of the pattern onthe semiconductor substrate with image signals of the reference pattern,for the semiconductor substrate which has reached a specified positionof the manufacturing line; a defect analyzing step for analyzing a causeof defect or a factor of defect which causes a defect of the pattern inthe manufacturing line located at an upper stream from the specifiedposition of the manufacturing line, according to the defect informationof the pattern detected in the defect inspection step and the historydata or the data base which shows the relation of causes and effects,built up in the history data or data base build-up step; and a processcondition control step for controlling process conditions in theabove-described upper stream manufacturing line to eliminate the causeof defect or the factor of defect analyzed in the defect analyzing step.

With the configuration described above, the present invention enablesinspection of micro fine defects with high resolution and highsensitivity on semiconductor substrates such as the semiconductor wafer,the TFT substrate, the thin film multi-layer substrate and the printedboard each having micro fine patterns (for example, patterns the pitchof which is 1 μm or under (0.8 to 0.4 μm)), to reduce the number ofmicro fine defects on the semiconductor substrates by feeding back theresults of inspection to the manufacturing processes for semiconductorsubstrates, and to manufacture the semiconductor substrates having microfine patterns with a high yield rate.

According to the present invention, for materializing a manufacturingmethod of the semiconductor substrate, a method and apparatus fordetecting a defect of the patterns on the object to be inspected areadapted to detect the pattern on the object to be inspected according tothe image signals of the pattern on the object to be inspected which areobtained by concentrating an annular-looped diffusion illumination lightformed by a plurality of virtual spot light sources and irradiating theillumination light onto the pattern on the object to be inspectedthrough the pupil of the objective lens. The above configuration enablessufficient introduction of the reflected light which is obtained byslantly or obliquely introducing a focused illumination light from, forexample, the annular-looped illumination onto a semiconductor substrate(object to be inspected), into the opening (pupil) of the objective lensand consequently obtain image signals of a pattern having a sufficientresolution, identify the reflected light by monitoring an image on thepupil plane of the objective lens, and detect the image signals of thepattern with the sufficient resolution and a large depth of the focusunder an optimum condition at all times in response to a micro finepattern by, for example, controlling the annular-looped illumination. Bydetecting a localization distribution or an intensity distribution ofthe reflected light from the image of the pupil plane (Fouriertransformation plane) and controlling the annular-looped illumination inaccordance with the localization distribution or the intensitydistribution (corresponding to the density of pattern) of the detecteddiffraction light, the pattern can be sufficiently inspected with anormal resolution by the annular-looped illumination under the presetcondition since the pattern density is not so high in a case of, forexample, a 4 Mb DRAM memory device and the pattern can be inspected withthe annular-looped illumination which provides a higher resolution underthe preset condition in a case of, for example, a 16 Mb DRAM memorydevice. In addition, the pattern can be inspected with high resolutionby using the annular-looped illumination under the preset conditionsince the pattern density is high at, for example, the cell part of thememory device and the pattern can be inspected at a high speed by usinga normal illumination since the inspection sensitivity can be lowered ina rough area other than the cell part.

Furthermore, for implementing the above-described semiconductorsubstrate manufacturing method, a method and apparatus for inspecting adefect of a pattern on the object to be inspected according to thepresent invention are adapted to concentrate and irradiate theannular-looped diffusion illumination light comprising a number ofvirtual spot light sources onto the pattern on the object to beinspected through the pupil of the objective lens, comparing an imagesignal obtained from of the pattern on the inspected object with theimage signal of the reference pattern, and erase the pattern on theinspected object when these image signals coincide, and detect a defectwhen these image signals do not coincide.

The above-described configuration enables detection of high definition(high resolution) image signals from micro fine patterns and inspectionof a defect on the micro fine pattern with high reliability since thehigh definition image signals can be compared with the high definitionreference image signals with respect to a chip or cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram arrangement showing an embodiment of aninspection apparatus according to the present invention for inspecting adefect of the pattern on the object to be inspected;

FIG. 2 is a schematic illustration of a disc type mask (annular-loopedsecondary light source) in the embodiment shown in FIG. 1;

FIG. 3 is a schematic illustration showing in detail the mask element ofthe disc type mask shown in FIG. 2;

FIG. 4 is a schematic illustration showing further in detail the maskelement of the disc type mask shown in FIG. 2;

FIGS. 5a and 5 b is an illustration showing practical dimensions of themask element shown in FIG. 4;

FIG. 6 is an illustration showing a grid pattern to be repeated in the Xaxis direction which is an embodiment of an LSI wafer pattern;

FIG. 7 is an X-Y plan view on the pupil of the objective lens, showing0th order diffraction light and first order diffraction light which areproduced in the X axis direction from the grid pattern shown in FIG. 6by casting the annular-looped illumination onto the grid pattern to beincident onto the pupil of the objective lens;

FIG. 8 is an X-Z cross sectional view showing the 0th order diffractionlight and the first order diffraction light which are produced from theannular-looped illumination and the grid pattern shown in FIG. 7 to beincident onto the pupil of the objective lens;

FIG. 9 is an X-Y plan view on the pupil of the objective lens, showing0th order diffraction light and first order diffraction light which areproduced in the Y axis direction from the grid pattern shown in FIG. 6by casting the annular-looped illumination onto the grid pattern to beincident onto the pupil of the objective lens;

FIG. 10 is an X-Y plan view on the pupil of the objective lens, showing0th order diffraction light and first order diffraction light which areproduced in X and Y axis directions from the grid pattern shown in FIG.6 by casting the annular-looped illumination onto the grid pattern to beincident onto the pupil of the objective lens;

FIG. 11 is an illustration showing the relationship between the value σand the incident angle ψ of the objective lens;

FIG. 12 is an illustration showing the relationship between the incidentangle ψ and the diffraction angle θ;

FIGS. 13(a) and 13(b) are illustrations of a linear diagram showing asituation where + first order diffraction light is produced when theannular-looped illumination with the wavelength of λ=0.4 to 0.6 μm andthe value σ of 0.60 to 0.40 is cast to a grid pattern of P=0.61 μm;

FIGS. 14(a) and 14(b) are illustrations a linear diagram showing asituation where +first order diffraction light is produced when theannular-looped illumination with the wavelength of λ=0.4 to 0.6 μm andthe value σ of 0.60 to 0.40 is cast to a grid pattern of P=0.7 μm;

FIG. 15 is an illustration showing a grid pattern to be repeated in theY axis direction which is an embodiment of the LSI wafer pattern;

FIG. 16 is an X-Y plan view on the pupil of the objective lens, showing0th order diffraction light and first order diffraction light which areproduced in the Y axis direction from the grid pattern shown in FIG. 15by casting the annular-looped illumination onto the grid pattern to beincident onto the pupil of the objective lens;

FIG. 17 is an Y-Z cross sectional view showing a state of attenuation of0th order diffraction light through an attenuation filter (lightquantity control filter);

FIG. 18 is an X-Y plan view on the pupil conjugated with the pupil ofthe objective lens showing a state of attenuation of the 0th orderdiffraction light through the attenuation filter (light quantity controlfilter) for which the contents shown in FIG. 17 are provided at aposition conjugated with the pupil of the objective lens;

FIGS. 19(a) and 19(b) is an illustration showing a cross sectional shapeof the attenuation filter (light quantity control filter) and itstransmissivity characteristic when the transmissivity is set to beapproximately 0;

FIGS. 20(a) and 20(b) is an illustration showing a cross sectional shapeof the attenuation filter (light quantity control filter) and itstransmissivity characteristic when the transmissivity is set to beapproximately 0.2;

FIG. 21 is a diagram showing an embodiment in which a light house iscontrolled in the optical axis direction for a collimator lens in theannular-looped illumination according to the present invention;

FIG. 22 is a diagram showing an embodiment in which a collimator lens iscontrolled in the optical axis direction for a light house lens in theannular-looped illumination according to the present invention;

FIG. 23 is a block diagram arrangement showing an embodiment of amicroscope system according to the present invention;

FIG. 24 is a diagram showing various defects in a wafer patternaccording to the present invention;

FIG. 25 is an illustration showing the relation to the dimensions of thepixel to be detected at a portion on the wafer pattern shown in FIG. 24;

FIGS. 26(a) and 26(b) show the pattern at the portion shown in FIG. 25and an image signal waveform corresponding to the brightness whichfaithfully represents this pattern;

FIGS. 27(a) and 27(b) show an image signal corresponding to a sampledbrightness obtained by sampling image signals corresponding to thebrightness shown in FIG. 26;

FIGS. 28(a) and 28(b) show an image signal waveform corresponding to abrightness which is faithfully obtained when the size of the pixel to bedetected is set to 0.0175 μm for a grid repetitive pattern comprisinglines of 0.42 μm in width and spaces;

FIGS. 29(a) and 29(b) show an image signal waveform corresponding to abrightness for which a maximal value is maintained when the size of thepixel to be detected is set to 0.14 μm for a grid repetitive patterncomprising lines of 0.42 μm in width and spaces;

FIGS. 30(a) and 30(b) show an image signal waveform corresponding to abrightness for which a maximal value is not maintained when the size ofthe pixel to be detected is set to 0.28 μm for a grid repetitive patterncomprising lines of 0.42 μm in width and spaces;

FIG. 31 illustrates an optical system in an embodiment of the patterninspection apparatus shown in FIG. 1 according to the present inventionfor inspecting a defect of the pattern on the object to be inspected;

FIG. 32 is a front view of FIG. 31;

FIG. 33 is a plan view further specifically showing the embodiment shownin FIG. 31;

FIG. 34 is a front view of FIG. 33;

FIG. 35 is a diagram showing an embodiment of an optical system forcircular polarization illumination;

FIG. 36 is a diagram for describing conversion from linear polarizationto circular or elliptic polarization with a ¼ wavelength plate;

FIG. 37 shows a detection intensity corresponding to the brightness fora pattern angle in an experimental example for which a state ofpolarization in the annular-looped illumination is controlled;

FIG. 38 shows a contrast for a pattern angle in an experimental examplefor which a state of polarization in the annular-looped illumination iscontrolled; and

FIG. 39 is a block diagram arrangement for describing manufacturing ofsemiconductor substrates at a high yield rate by analyzing causes ofdefect or factors of defect with an analytical computer according to thepresent invention and feeding back the causes of defect or the factorsof defect which has been analyzed to the process units in amanufacturing line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, like reference numerals are utilized todesignate like parts throughout so that detailed description of the likeparts are omitted with embodiments according to the present inventionfor detection of a pattern on an object to be inspected and inspectionof a defect on the pattern being described, referring to FIGS. 1 to 39,and an embodiment according to the present invention in which inspectionof a defect on the object to be inspected is applied to semiconductormanufacturing processes being described referring to a FIG. 39. In theembodiments, an annular-looped illumination (annular-looped diffusionillumination) is utilized for providing substantially uniformillumination in a field of detection of the object to be inspectedthrough an objective lens is described below.

FIG. 1 is a block diagram showing a first embodiment of a patterninspection apparatus using annular-looped illumination according to thepresent invention comprising an object to be inspected (a pattern to beinspected) 1 such as an LSI wafer for pattern inspection; an XYZθ stage2 on which the object to be inspected 1 such as the LSI wafer ismounted; a secondary light source for annular-looped illumination whichincludes a xenon (Xe) lamp 3 for a light source, an elliptic mirror 4for focusing a light and a disc type mask 5 (secondary light source forannular-looped illumination) for forming an annular-looped illumination(annular-looped diffusion illumination) for forming an annular-loopedsecondary light source which includes a plurality of virtual spot lightsources; an illumination optical system including a collimator lens 6, alight quantity control filter 14 and a condenser lens 7; a patterndetection optical system which includes half mirrors 8 a and 8 b , anobjective lens 9, a focusing lens 11, a zoom lens 13 provided with anattenuation filter 38 on a pupil plane 10 b conjugated with the pupilplane 10 a of the objective lens 9 and two-dimensional orone-dimensional image sensors 12 a and 12 b; and an image processing andcontrolling system for detection of defects, which includes A/Dconverters 15 a and 15 b for converting image signals detected from theimage sensors 12 a and 12 b to digital image signals, a delay memory 16for storing digital image signals obtained from the A/D converter 15 aand delaying these image signals, a comparator circuit 17 for comparingdelayed digital image signals stored in the delay memory 16 and digitalimage signals obtained from the A/D converter 15 a , an edge detector 21for detecting an edge of the pattern from the digital image signalsobtained from the A/D converter 15 a, and a CPU 20 which carries out thecontrol of the disc type mask 5 for forming the annular-loopedillumination which is the secondary light source based on a movingmechanism 19 and the control of the attenuation filter 38 based on amoving mechanism 39 in accordance with the digital image signals on thepupil plane 10 a of the objective lens 9 obtained from the image sensor12 b, which detects the image of the pupil plane 10 a of the objectivelens 9 through the A/D converter 15 b, carries out the comparison in thecomparator circuit 17 in accordance with the edge signal to be detectedby the edge detector 21 and carries out the control of the XYZθ stage 2based on a driver 45.

A defect determination output 18 is obtained from the comparator circuit17 and is also entered into the CPU to be added with a defect occurringposition (coordinates) on the object 1 to be inspected and is stored instorage arrangement (not shown) for at least a unit of the inspectedobject 1 and a unit of a plurality of inspected objects 1 sampled from aspecified manufacturing process. Defect information 40 in at least theunit of the inspected object 1 and the process unit of the inspectedobject 1 sampled from the specified manufacturing process which isstored in this storage means is outputted from the CPU 20. This defectinformation 40 includes the defect occurring position (coordinates) onthe inspected object 1 obtained based on the defect determination output18 and a type of defect (projection defect 231, chipping defect 236,opening defect 232, short-circuiting defect 234, discoloration defect233, stain defect 235, etc., as shown in FIG. 24, for example) which isclassified according to the defect determination output 18 in the CPU 20as shown in FIG. 23. The types of these defects need not always bedefinitely classified.

In FIG. 1, a light house 124 is formed with the Xe lamp 3 which is theprimary light source, the elliptic mirror 4 for focusing a light emittedfrom the Xe lamp 3 and the disc type mask 5 comprising a plurality ofvirtual spot light sources, for forming the annular-looped illuminationas the secondary light source. The moving mechanism 19 is provided torotate the disc type mask (secondary light source for annular-loopedillumination) 5 in steps according to a command from the CPU 20 and tochange over a different type annular-looped illumination (if there is noIN σ as shown, for example, in FIG. 3, it is similar to normalillumination). The disc type mask 5 is the annular-looped secondarylight source formed by a plurality of virtual spot light sources and anannular-looped diffusion illumination is obtained from thisannular-looped secondary light source.

Accordingly, the annular-looped illumination emitted from the disc typemask (secondary light source for annular-looped illumination) 5 isfocused as an incident illumination light 24 onto the pupil 10 a of theobjective lens 9 through the collimator lenses 6 and 7 as shown in FIGS.7, 9 and 10, and this focused incident illumination light is focused bythe objective lens 9 and irradiated onto the inspected object 1 such asan LSI wafer set on the XYZθ stage 2 (the θ stage not being shown). Thelight quantity control filter 14 serves to adjust a light quantity to beirradiated onto the inspected object 1. A drive mechanism 14 a fordriving the light quantity adjusting filter 14 is controlled inaccordance with a command from the CPU 20.

A 0th order reflected diffraction light (positive reflection light), andfirst order and second order reflected diffraction lights at the + and −sides are produced from the pattern on the inspected object 1 such asthe LSI wafer. Thus, of the 0th order reflected diffraction light(positive reflection light) and + and − side first order and secondorder reflected diffraction lights produced as described above, areflected diffraction light which is introduced into the pupil 10 a ofthe objective lens 9 is reflected from the half mirrors 8 a and 8 b tobe incident onto the pupil 10 b of the zoom lens 13 and this reflecteddiffraction light is focused onto the image sensor 12 a by the zoom lens13. The image sensor 12 a receives the reflected diffraction light whichis produced from the pattern on the inspected object 1 such as the LSIwafer and introduced to be incident into the pupil 10 a of the objectivelens 9, and outputs an image signal representing the reflecteddiffraction light of the pattern of the inspected object 1. The pupil 10a of the objective lens 9 and the pupil 10 b of the zoom lens 13 have aconjugating relationship. The 0th order diffraction light introducedinto the pupil 10 a of the objective lens 9 can be attenuated by theattenuation filter 38 on the pupil 10 b of the zoom lens 13 as required.

On the other hand, the reflected diffraction light introduced into thepupil 10 a of the objective lens 9 is focused onto the image sensor 12 bthrough the focusing lens 11. Accordingly, the image sensor 12 breceives the reflected diffraction light introduced into the pupil 10 aof the objective lens 9 and outputs the image signal of this reflecteddiffraction light to permit detection of a state of the reflecteddiffraction light incident into the pupil 10 a of the objective lens 9.In other words, if the periodicity of the pattern on the inspectedobject 1 such as the LSI wafer changes as shown in FIGS. 13 and 14, themode of the first order diffraction light to the incident illuminationlight 24 also changes and the first order diffraction light incidentinto the pupil 10 a of the objective lens 9 changes simultaneously. FIG.13 shows a case where the density (periodicity) of the pattern on theinspected object 1 is high and FIG. 14 shows a case where the density(periodicity) of the pattern on the inspected object 1 is low. If thepitch P (density or periodicity) of the pattern on the inspected object1 or the wavelength λ of the incident illumination light 24 is changed,it is known from a relation presented by equation 2 that the diffractionangle θ of the first order diffraction light to the incident angle ψ ofthe incident illumination light 24 changes and the first orderdiffraction light incident into the pupil 10 a of the objective lens 9also changes.

If the type of the inspected object 1 such as, for example, the LSIwafer is changed, the pitch P (density or periodicity) of the patternthereon also changes. If the type of the LSI wafer is changed to, forexample, 256M DRAM or 64M DRAM, the pitch P (density or periodicity) ofthe pattern also changes. If the process is changed even though thetypes are of the same, the density (periodicity) of the pattern maychange, for example, the pitch P of the pattern of the inspected objectin the wiring process or the diffusion process changes. In one chip onthe LSI wafer, the pitches P of the patterns of the memory and theperipheral circuit differ from each other.

It is necessary to change the wavelength λ of the incident illuminationlight 24 in accordance with the cross sectional structure of theinspected object 1. For example, a thickness of a thin film which formsthe inspected object 1 varies and therefore the reflected light from theinspected object is caused to change due to an optical interference inthe thin film. To avoid such variation of the reflected light, it isnecessary to change the wavelength λ of the incident illumination light24 to select the wavelength λ of the incident illumination light 24 withwhich the optical interference hardly occurs in the thin film. Forexample, as shown in other embodiments described later, the wavelength λof the incident illumination light 24 can be changed through awavelength selection filter by using a light source which emits lights,respectively, having a plurality of types of wavelength in theillumination optical system.

If the pitch P (density or periodicity) of the pattern on the inspectedobject 1 or the wavelength λ of the incident illumination light 24 ischanged, the diffraction angle θ of the first order diffraction light tothe incident angle ψ of the incident illumination light 24 changes andthe first order diffraction light incident into the pupil 10 a of theobjective lens 9 also changes. Therefore, the value σ of the secondarylight source for annular-looped illumination, that is, the incidentangle ψ of the illumination light 24 to the inspected object 1 should becontrolled in accordance with the type or the cross sectional structureof the inspected object 1 so that, particularly, the first orderdiffraction light of the diffraction lights produced from the inspectedobject is introduced into the pupil 10 a of the objective lens 9 in anoptimal condition.

Therefore, the CPU 20 carries out a Fourier transform image analysis ofdigital Fourier transform image signals on the pupil 10 a (Fouriertransform plane) of the objective lens 9 obtained from the image sensor12 b through the A/D converter 15 b and edge density determination(periodicity or density determination of the pattern on the inspectedobject 1) according to the results of this Fourier transform imageanalysis, and selects the secondary light source 5 (as shown, forexample, in FIGS. 3 and 4; FIG. 4 includes an ordinary light source withIN σ of 0) for the optimum annular-looped illumination by driving themoving mechanism 19 so that the digital image signal of the reflecteddiffraction light introduced into the pupil 10 a of the objective lens9, that is, the 0th order and first order diffraction lights from thepattern on the inspected object 1 are sufficiently introduced into thepupil 10 a of the objective lens 9 to obtain faithful image signals fromthe pattern on the inspected object 1 from the image sensor 12 a.

Illumination is the so-called Koehler illumination free of unevenness.Although not shown, the illumination light is focused so that the imageof the reflected diffraction light from the pattern on the inspectedobject 1 such as the LSI wafer is clearly formed in the image sensor 12a. In other words, the pattern (surface) on the inspected object 1 suchas the LSI wafer is automatically focused to the detection opticalsystem.

Two-dimensional image signals of the pattern on the inspected object 1can be obtained from the image sensor 12 a by scanning to pick up thepattern image with the image sensor 12 a while moving the X stage onwhich the inspected object 1 such as the LSI wafer is set. In this case,the X stage can be moved in continuous feed, step feed or repeated feed.

The two-dimensional image signals obtained as described above areA/D-converted by the A/D converter 15 a, two-dimensional digital imagesignals are stored in the delay memory 16 to be delayed while inspectionof the chip or the cell is repeated, and the delayed two-dimensionaldigital image signals and the two-dimensional digital image signalsoutputted from the A/D converter 15 a are compared with respect to thechip or the cell by the comparator circuit 17, and unmatched digitalimage signals are detected as a defect 18.

The above-described comparator circuit 17 is known in the art andtherefore a detailed description is omitted and it is briefly describedbelow. This comparator circuit 17 is adapted so that two-dimensionallight and dark image signals (digital image signals) obtained from thedelay memory 16 and the A/D converter 15 a with respect to the patternson the inspected object 1 which are formed to be identical aredifferentiation-processed, the positions of two light and dark imagesignals to be compared are aligned so that the number of pixels whosepolarities do not match is not more than a preset value when thepolarities of these light and dark image signals obtained from suchdifferentiation processing are compared, a differential image signal ofthe two light and dark image signals the positions of which are alignedis detected, and a defect is detected by binary-coding this differentialimage signal with a desired threshold value. The comparison processingin this comparator circuit 17 is described in detail in Japanese PatentLaid-Open No. Hei 3-209843.

The edge detector 21 detects an edge of the pattern on the inspectedobject 1 according to the two-dimensional digital image signal which isdetected by the image sensor 12 a and obtained through the A/D converter15 a. The CPU 20 is able to align the positions of two light and darkimage signals (digital image signals) in the comparator circuit 17 byfetching the edge information of the pattern on the inspected object 1detected by the edge detector 21 and feeding back the information to thecomparator circuit 17 and compare these signals with respect to the chipand the cell by controlling the timing read out from the delay memory16.

It is apparent that the comparator circuit 17 is not limited to theabove-described configuration and a comparator circuit with anotherconfiguration can be used.

A two-dimensional digital image signal at a position on the designatedstage coordinates obtained from the A/D converter 15 a can be stored inthe delay memory 16 and the CPU is able to read out and analyze thissignal. Particularly, if the inspected object 1 includes a defect, thecharacteristics of the defect can be analyzed and therefore the optimuminspection conditions can be found.

The disc type mask (secondary light source for annular-loopedillumination) 5 for forming the annular-looped illumination is nowdescribed referring to FIGS. 2 to 5, wherein FIG. 2 is a schematicillustration of the disc type mask (an array of many kinds of maskelements for annular-looped illumination) in the embodiment shown inFIG. 1. FIG. 3 shows a practical embodiment of the disc type mask (anarray of many kinds of mask elements for annular-looped illumination)shown in FIG. 2. FIG. 4 shows another practical embodiment of the disctype mask (an array of many kinds of mask elements for annular-loopedillumination) shown in FIG. 2 and FIGS. 5(a) and 5(b) are diagrams forillustrating the mask element for one annular-looped illumination shownin FIGS. 3 and 4.

As shown in FIG. 2, mask elements 5-1, 5-2, . . . , 5-n, for example,for many types of annular-looped illuminations are provided on the disctype mask 5 and the disc type mask 5 is changed over by the movingmechanism 19 which serves to rotate the disc type mask 5. FIG. 3 showsin detail the mask elements 5-1, 5-2, . . . , 5-n for many types ofannular-looped illuminations shown in FIG. 2 with 5 a-1, 5 a-2, . . . ,5 a-n. In FIG. 3, 5 a-1 denotes a ring-shaped mask element on which aportion between IN σ and OUT σ is made to be transparent, 5 a-2 shows aring-shaped mask element on which IN σ and OUT σ are made to be largerthan those of 5 a-1, and 5 a-n shows a ring-shaped mask element in whicha portion of a ring-shaped transparent part is shielded.

FIG. 4 shows in detail the mask elements 5-1, 5-2, . . . , 5-n for manytypes of annular-looped illuminations shown in FIG. 2 with 5 b-1, 5 b-2,5 b-3, 5 b-4, 5 b-5, 5 b-6, 5 b-7, 5 b-8, 5 b-9, and 5 a-10. 5 b-1 showsa ring-shaped mask element on which a portion between IN σ of 0.6 andOUT σ of 1.0 is made transparent, 5 b-2 shows a ring-shaped mask elementon which a portion between IN σ of 0.4 and OUT σ of 1.0 is madetransparent, 5 b-3 shows a ring-shaped mask element on which a portionbetween IN σ of 0.2 and OUT σ of 1.0 is made transparent, 5 b-4 shows aring-shaped mask element on which a portion between IN σ of 0.4 and OUTσ of 0.8 is made transparent, 5 b-5 a ring-shaped mask element on whicha portion between IN σ of 0.2 and OUT σ of 0.8 is made transparent, 5b-6 a ring-shaped mask element on which a portion between IN σ of 0.4and OUT σ of 0.6 is made transparent, and 5 b-7 shows a ring-shaped maskelement on which a portion between IN σ of 0.2 and OUT σ of 0.6 is madetransparent. The ring-shaped mask elements 5 b-1 to 5 b-7 form thesecondary light source for the annular-looped illumination.

In FIG. 4, 5 b-8 shows a mask element which is formed with a circulartransparent part for which the value σ is 0.89, 5 b-9 shows a maskelement which is formed with a circular transparent part for which thevalue σ is 0.77, and 5 b-10 shows a mask element which is formed with acircular transparent part for which the value σ is 0.65. These maskelements 5 b-8 to 5 b-10 form an ordinary secondary light source withdifferent values σ. The value σ of 1.0 indicates that it is equal to anaperture NA (Numerical Aperture) corresponding to the diameter of thepupil of the objective lens 9.

FIGS. 5(a) and 5(b) are diagrams for showing practical dimensions of thering-shaped mask elements shown in FIG. 4, wherein M is a surface of anopaque mask which shuts off the light and shows IN σ and OUT σ. FIG.5(b) shows the thickness t of the mask which is assumed as 2.3 mm. Thediameters of OUT σ and IN σ of the ring-shaped mask elements of 5 b-1 to5 b-7 are shown in Table 1 below.

TABLE 1 Part No. Diameter of OUT σ Diameter of IN σ 5b-1 5.25 mm 3.15 mm5b-2 5.25 mm 2.10 mm 5b-3 5.25 mm 1.05 mm 5b-4 4.20 mm 2.10 mm 5b-5 4.20mm 1.05 mm 5b-6 3.15 mm 2.10 mm 5b-7 3.15 mm 1.05 mm

The inside part of IN σ is made to be opaque in the above-describedring-shaped mask elements. When it is made opaque, the light quantityreduces and therefore the inside part of IN σ can be made to be opaqueto conform to the patterns on the high density inspected object 1without substantially reducing the light quantity. The part between IN σand OUT σ can be substantially transparent. Although, in the aboveembodiment, the part between IN σ and OUT σ is formed with a ring-shapedtransparent member, it is obvious that the part can be formed byarranging a plurality of circular transparent members in the shape ofring.

As described above, many kinds of secondary or virtual light sources canbe formed by forming many types of mask elements on the disc type mask 5and therefore an appropriate incident illumination light for variousinspected objects 1 can be obtained. Consequently, the 0th orderdiffraction light and the first order diffraction light (+ first orderdiffraction light or − first order diffraction light) obtained fromvarious inspected objects 1 can be introduced into the opening (pupil)10 a of the objective lens 9 and two-dimensional image signals having asufficient resolution for various inspected objects 1 can be obtainedfrom the image sensor 12 a.

Two-dimensional image signals having a sufficient resolution for a highdensity pattern on the inspected object can be obtained by using theannular-looped illumination for the following reason. In case ofordinary illumination, the incident angle ψ of an incident illuminationlight 30 shown in FIG. 12 is approximately 0. In a case that the pitch Pof the inspected object 1 is small (in case of a high density pattern),the diffraction angle θ of the 0th order diffraction light (m=0) isequal to the incident angle ψ to be within the pupil 10 a of theobjective lens 9 for the relation represented by the equation 2.However, the diffraction angles θ of the + first order diffraction lightand the − first order diffraction light become large because theabove-described pitches P is small, and cannot therefore be introducedinto the pupil 10 a of the objective lens 9. Accordingly, only the 0thorder diffraction light, that is, the light of the DC component, isobtained from the high density pattern on the inspected object and theimage based on the diffraction light cannot be obtained from the patternon the inspected object.

The above relationship can be further described in detail according tothe Abbe's diffraction theory. In other words, the Abbe's diffractiontheory applies to the relationship between the incident angle ψ to theoptical axis of the incident illumination light 30 and the spacefrequency to be focused.

Whether a grid pattern on the inspected object can be focused depends onwhether the first order diffraction light from the grid pattern on theinspected object can pass through the pupil 10 a of the imaging system(objective lens 9). If the focusing point remains inside the pupil 10 awhen a diffraction light 31 is focused onto one point of the pupil 10 aof the imaging system (objective lens 9), the diffraction light passesthrough the imaging system (objective lens 9) and interferes with the0th order diffraction light on the imaging plane to form the image ofthe grid pattern. This configuration is advantageous in that a focaldepth can be larger.

When the structure of the grid pattern on the inspected object is fine(the pitch P becomes small), the angle θ of the first order diffractionlight to the optical axis becomes large and, when the angle θ is largerthan NA of the imaging system (objective lens 9), the first orderdiffraction light cannot pass through the pupil 10 a of the imagingsystem (objective lens 9) and the image of the grid pattern will not beformed.

Although the resolution is improved in a plane between the optical axisand the light source in a simple slanted illumination, the resolution isnot improved in other planes. To improve the resolution in an optionaldirection, it is necessary to apply the annular-looped illumination asdescribed above and prevent an incident illumination light, the firstorder diffraction light of which is not introduced into NA of theimaging system (objective lens 9) from being introduced in accordancewith the direction of the pattern on the inspected object.

A method of illumination in which the 0th order diffraction light doesnot enter into the pupil 10 a of the imaging system (objective lend 9)corresponds to the so-called dark field illumination. If there is onlythe first order diffraction light in the opening of the imaging system(objective lens 9) with the dark field illumination as described above,the resolution is extremely low.

In FIG. 1, the CPU 20 controls the annular-looped illumination accordingto the information detected by the image sensor 12 b, which serves as amonitor for the pupil 10 a of the objective lens 9, by driving themoving mechanism 19 to change over the light source for theannular-looped illumination comprising the disc type mask 5 (secondarylight source for annular-looped illumination) so that the first orderdiffraction light and the 0th order diffraction light always enter intothe pupil 10 a of the objective lens 9 even when the pattern of theinspected object 1 changes. Specifically, the CPU 20 uses the image ofthe Fourier transform plane (the surface of the pupil 10 a of theobjective lens 9) detected by the image sensor 12 b and controls theannular-looped illumination to shut off the incident illumination light,a first order diffraction light 23 of which does not enter into thepupil 10 a of the objective lens 9, or lowers the intensity of theincident illumination light in accordance with the pattern of theinspected object 1 by driving and controlling the moving mechanism 19 tochange over the disc type mask 5 to 5 a-1, 5 a-2, . . . , or 5 b-1, 5b-2, . . .

However, if the periodicity is not observed in the pattern of theinspected object, that is, in a case of a diffraction light (diffractioncomponents are continued) having various diffraction angles in a widespread, the pattern can be regarded as an isolated pattern (noperiodicity is observed) and therefore excessively slanted introductionof the incident illumination light is avoided and the illumination fromthe secondary light source for an appropriate annular-loopedillumination (mask elements 5 b-4, 5 b-5, 5 b-6 and 5 b-7 (with smallOUT σ) on the disc type mask 5 shown in FIG. 4) or the light source foran ordinary circular illumination (mask elements 5 b-8, 5 b-9 and 5b-10) is selected.

The edge detector 21 differentiates the image signals of the pattern ofthe inspected object 1 detected by the image sensor 12 a and detects theedge information of the pattern of the inspected object 1 throughprocessing of the threshold value. Accordingly, the CPU 20 calculatesthe width of the pattern of the inspected object 1 by calculating, forexample, an area surrounded by the edge of the pattern according to theedge information of the inspected object 1 detected by the edge detector21, then calculates the density (pitch P) of the pattern of theinspected object 1 according to the pattern width of this inspectedobject 1, and controls the annular-looped illumination by driving andcontrolling the moving mechanism 19 and changing over the light sourcefor the annular-looped illumination which comprises the disc type mask 5in accordance with the calculated density (pitch P) of the pattern ofthe inspected object 1. For example, when the density of the pattern ishigh, the incident illumination light is introduced at a more slantedangle.

Specifically, the CPU 20 compares the density of the pattern of theinspected object 1 to be calculated with a preset value, controls theannular-looped illumination in accordance with the density of thepattern or selects the mask elements 5 b-1, 5 b-2 and 5 b-3 (with alarger OUT σ) shown in FIG. 4 as the light source for the annular-loopedillumination so that a slanted incident component is increased as thedensity of the pattern is higher.

The control of the annular-looped illumination by the CPU 20 can becarried out under a predetermined or preset condition (information as tothe type of pattern of the inspected object 1 to be entered by inputunit 32 and mounted on the stage 2 or information as to the typeincluding the process of the inspected object 1 to be obtained from thehost computer which controls the manufacturing processes for theinspected object 1 and mounted on the stage 2). In other words, it isnecessary to control the annular-looped illumination so as to use theannular-looped illumination available under the preset condition (anannular-looped illumination approximate to a circular illumination (maskelements 5 b-4, 5 b-5, 5 b-6 and 5 b-7 (with a smaller OUT σ)) on thedisc type mask 5 shown in FIG. 4) or a circular illumination (maskelements 5 b-8, 5 b-9 and 5 b-10 shown in FIG. 4) since the density ofthe pattern is not so high and the pattern can be identified with a lowresolution in a case that the type of the inspected object 1 to bemounted on the stage 2 is, for example, a 4 Mb DRAM memory element, andto use the annular-looped illumination which provides a high resolutionunder the preset conditions (mask elements 5 b-1, 5 b-2, and 5 b-3 (witha larger OUT σ) shown in FIG. 4) since a high density pattern should bedetected with the high resolution in a case that the type of theinspected object 1 is the 16 Mb DRAM memory element.

If a mask element with the value σ of approximately 0.5 smaller thanthat of the mask element 5 b-10 (σ is 0.65) shown in FIG. 4 is used inthe circular illumination, the image sensor 12 a receives an image of adeep groove or hole and image signals with high contrast of a patternincluding deep grooves or holes can be obtained.

For example, the cell part of the memory element where the patterndensity is high can be inspected with the annular-looped illuminationwhich provides a high resolution under the preset condition and roughareas other than the cell part can be inspected with the ordinarycircular illumination so that the inspection sensitivity is notdeteriorated (so that the intensity of the incident illumination lightis not reduced).

Thus, various patterns (circuit patterns) can be detected with highresolution and sensitivity with the objective lens (imaging opticalsystem) 9 by using various modes of annular-looped illuminationsincluding the circular illumination and particularly, the annular-loopedillumination can apply to high density patterns on which the degree ofintegration is increased. The NA of the objective lens (imaging opticalsystem) 9 need not be larger than required so as not to suffice thefocal depth.

In a case that the first order diffraction light is prevented fromentering into the pupil 10 a of the objective lens 9 by, for example,the attenuation filter 38 for partly controlling the light intensityprovided at a position 10 b conjugated with the pupil 10 a of theobjective lens 9, the 0th order diffraction light which reaches theattenuation filter 38 through the pupil 10 a of the objective lens 9 isshut off or the intensity of this diffraction light is reduced. In acase that the + first order, − first order and 0th order diffractionlights are introduced into the pupil 10 a of the objective lens 9, theintensities of the first order and 0th order diffraction lights arecontrolled to be coincided by, for example, the attenuation filter 38for partly controlling the light intensity.

The CPU 20 is able to partly control the transmissivity (attenuationratio) by driving and controlling the moving mechanism 39 and changingover the attenuation filter 38 according to the information detected bythe image sensor 12 b, which serves a monitor for the pupil 10 a of theobjective lens 9, to make the image sensor 12 a balance and receive the0th order diffraction light and the first order diffraction light inaccordance with the pattern of the inspected object 1.

The detection of the grid pattern in the LSI wafer patterns as shown inFIG. 6 is now described as an example of the inspected object 1 withhigh resolution by using the annular-looped illumination. FIG. 6 is aschematic diagram showing a grid pattern comprising lines and spaces ina peripheral circuit of the LSI wafer pattern. In FIG. 6, 101 is apattern line (a wiring pattern including a gate) which extends in the Yaxis direction. This grid type pattern line 101 is repeated at the pitchP in the X axis direction. A space (which may be formed with insulation)is formed between the pattern lines 101.

FIG. 7 is a schematic illustration showing, on the pupil 10 a of theobjective lens 9, the incident annular-looped illumination 24 forilluminating the grid pattern shown in FIG. 6, and 0th order diffractionlight 22 a, + first order diffraction light 25 a and − first orderdiffraction light 26 a obtained from reflection of incident illuminationlight 24 a onto the X-Z plane passing through the optical axis 33 fromthe grid pattern shown in FIG. 6. FIG. 8 is a schematic illustrationshowing the 0th order diffraction light 22 a , the + first orderdiffraction light 25 a and the − first order diffraction light 26 aobtained on the X-Z plane passing through the optical axis 33 fromreflection of the incident illumination light 24 a shown in FIG. 7 fromthe grid pattern shown in FIG. 6.

As shown in FIGS. 7 and 8, in the pupil 10 a of the objective lens 9,the 0th order diffraction light 22 a and the + first order diffractionlight 25 a are observed as having an area and as not being points on animage detected by the image sensor 12 b which serves as the monitor forthe pupil 10 a of the objective lens 9. Reference numeral 34 denotes therange of the annular-looped illumination 24 on the grid pattern of theLSI wafer.

In a case that the grid pattern of the LSI wafer extends in the Y axisdirection as shown in FIG. 6, the incident angle ψ of the incidentillumination light 24 a and the emission angle θ of the 0th orderdiffraction light 22 a are equal for the relationship represented by theequation 2 described later and the 0th order diffraction light 22 a isgenerated at a position symmetrical to the incident illumination light24 a as shown in FIGS. 7 and 8, and the + first order diffraction light25 a and the − first order diffraction light 26 a are generated at leftand right positions for the relationship represented by the equation 2.Since the grid pattern of the LSI wafer extends in the Y axis direction,the + first order diffraction light 25 a and the − first orderdiffraction light 26 a are generated at left and right positions in thepupil but not generated at upper and lower positions therein and areweak if generated. However, as apparent from FIGS. 7 and 8, not only the0th order diffraction light 22 but the + first order light 25 or the −first order diffraction light 26 can always be entered into the pupil 10a of the objective lens 9 by using the annular-looped illumination 24,and the image signals of the grid pattern of the LSI wafer can bedetected with high resolution by the image sensor 12 a.

FIG. 9 is a schematic illustration showing, on the pupil 10 a of theobjective lens 9, the incident annular-looped illumination 24 forilluminating the grid pattern shown in FIG. 6, and 0th order diffractionlight 22 b, + first order diffraction light 25 b and − first orderdiffraction light 26 b obtained from reflection of incident illuminationlight 24 b onto the Y-Z plane passing through the optical axis 33 fromthe grid pattern shown in FIG. 6. In other words, since the grid patternof the LSI wafer extends in the Y axis direction, the incident angle ψof the incident illumination light 24 b and the emission angle θ of the0th order diffraction light 22 b are equal for the relationshiprepresented by the equation 2 described later and the 0th orderdiffraction light 22 b is generated at a position symmetrical to theincident illumination light 24 b, and the + first order diffractionlight 25 b and the − first order diffraction light 26 b are introducedinto the pupil 10 a of the objective lens 9 as shown in FIG. 9.

However, since the grid pattern of the LSI wafer extends in the Y axisdirection, the + first order diffraction light 25 b and the − firstorder diffraction light 26 b are weak even though these diffractionlights enter into the pupil 10 a of the objective lens 9 and do nottherefore make a great contribution to the resolution of the gridpattern of the LSI wafer, and the annular-looped illumination in the Yaxis direction can be eliminated by using the mask element 5 a-n shownin FIG. 3. Although the first order diffraction light 23 b becomesweaker than the 0th order diffraction light 22 b, the resolution of thegrid pattern of the LSI wafer does not deteriorate considerably eventhough the 0th order diffraction light 22 b is entered into the pupil 10a of the objective lens 9 and received by the image sensor 12 a, whenboth the + first order diffraction light 25 b and the − first orderdiffraction light 26 b are entered into the pupil 10 a of the objectivelens 9 as shown in FIG. 9.

FIG. 10 is a schematic illustration showing, on the pupil 10 a of theobjective lens 9, incident annular-looped illumination light 24 forilluminating the grid pattern shown in FIG. 6, and 0th order diffractionlights 22 a′ and 22 b′, + first order diffraction lights 25 a′ and 25 b′and − first order diffraction lights 26 a′ and 26 b′ obtained fromreflection of incident illumination lights 24 a and 24 b on the X-Z andY-Z planes passing through the optical axis 33 from the grid patternshown in FIG. 6, in a case that OUT σ and IN σ of the annular-loopedillumination are respectively made larger than those shown in FIGS. 7 to9 for the pupil 10 a (NA) of the objective lens 9.

In a case that OUT σ and IN σ of the annular-looped illumination arerespectively made larger than those shown in FIGS. 7 to 9 for the pupil10 a (NA) of the objective lens 9 as shown in FIG. 10, the + first orderdiffraction lights 25 b′ and the − first order diffraction lights 26 b′are not entered into the pupil 10 a and, when the 0th order diffractionlight 22 b′ is received by the image sensor 12 a, the resolution for thegrid pattern is deteriorated. Therefore the 0th order diffraction light22 b′ faced in the Y axis direction can be prevented from beinggenerated by using the mask element 5 a-n shown in FIG. 3 to eliminatethe annular-looped illumination in the Y axis direction.

The 0th order diffraction light 22 b′ can be prevented from beingreceived by the image sensor 12 a by providing, for example, attenuationfilter 38 for partly controlling the same light intensity as the maskelement 5 a-n shown in FIG. 3 at a position 10 b in conjugation with theposition of the pupil 10 a of the objective lens 9 and shutting off the0th order diffraction light 22 b′ faced to the Y axis direction. Theconfiguration as described above enables detection of the grid patternwith high resolution by the image sensor 12 a even with theannular-looped illumination of which OUT σ and IN σ are respectively setto be large for the pupil 10 a (NA) of the objective lens 9.

Although, in the embodiment shown in FIG. 10, it is described that OUT σand IN σ are respectively set to be larger than those shown in FIGS. 7to 9 for the pupil 10 a (NA) of the objective lens 9, also in a casethat the pupil 10 a (NA) of the objective lens 9 is set to be smallerthan that shown in FIGS. 7 to 9 while retaining the sizes of OUT σ andIN σ the same as those in FIGS. 7 to 9, a state of generation of thediffraction light entered into the pupil 10 a (NA) of the objective lens9 is as shown in FIG. 10 and it is necessary to prevent the 0th orderdiffraction light 22 b′ from being received by the image sensor 12 a. Ina case that the pitch P of the grid pattern is finer than that shown inFIGS. 7 to 9 and the wavelength λ of the annular-looped illuminationlight is longer than that shown in FIGS. 7 to 9, generation of thediffraction light entering into the pupil 10 a (NA) of the objectivelens 9 is as shown in the embodiment in FIG. 10, and it is necessary toprevent the 0th order diffraction light 22 b′ from being received by theimage sensor 12 a as known from the relationship represented by theequation 2 described later.

A diffraction phenomenon obtained from the grid pattern with theannular-looped illumination is now described in the relationship betweenthe value σ of an optional annular-looped illumination and the incidentangle ψ to the optical axis 33 being described with reference to FIGS.11 and 12. Specifically, FIG. 11 is an illustration showing therelationship between the value σ of the objective lens 9 to the opticalaxis 33 and the incident angle ψ of the incident illumination lightirradiated onto the grid pattern surface of the inspected object 1 andFIG. 12 is an illustration showing the relationship between the incidentangle ψ and the emission angle (diffraction angle) σ of the diffractionlight 31.

In FIG. 11, the value σ of the annular-looped illumination lightincident into the pupil 10 a of the objective lens 9 and the incidentangle ψ of the incident illumination light irradiated onto the inspectedobject 1 are given by the equations shown below:

σ1:σ2=sinψ1:sinψ2

sinψ2=(σ2/σ1)×sinψ1

In this examination, the objective lens 9 for which chromatic aberrationis compensated and magnification of ×40 and NA=0.8 are given is used.

In this objective lens 9, the maximum incident angle satisfiesNA=sinψmax=0.8 in case of σ=1.0. In otherwords, σ=1.0 indicates NA(opening) (emission pupil) of the objective lens 9.

sinψ=(σ/1)×0.8=0.8σ

According to the above relationship, the incident angle ψ can beobtained from the relationship represented by equation 1.

ψ=sin−1(0.8σ)  (Equation 1)

The relationship between the incident angle ψ and the diffraction angleθ is described below.

In FIG. 12, the diffraction angle θ of the m-th order diffraction light31 has the relationship given by equation 2.

P=mλ/(sinψ-sin θ)

sinθ=sinψ-mλ/P

θ=asin(sinψ-mλ/P)  (Equation 2)

where λ is a wavelength (μm) of the illumination light, θ is adiffraction angle (emission angle), P is a pattern pitch (μm) and m is ssequential number of the diffraction light. In the equation 2, “asin”denotes “arc sin”.

Theoretical values (incident angle ψ and diffraction angle θ ) to thevalue σ of the annular-looped illumination light when the wavelength λand the pattern pitch P of the inspected object are changed according tothe above equations 1 and 2 are given by Tables 2, 3, 4 and 5 below.

TABLE 2 σ 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 Incidentangle ψ 53.13 46.05 39.79 34.06 28.69 23.58 18.66 13.89 9.21 4.59 −first order — — — — — — 77.35 63.60 54.66 47.37 diffraction light +first order 8.29 3.68 −0.90 −5.40 −10.13 −14.83 −19.62 −24.57 −29.72−35.15 diffraction light λ = 0.4 μm P = 0.61 μm (256 Mb)

TABLE 2 σ 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 Incidentangle ψ 53.13 46.05 39.79 34.06 28.69 23.58 18.66 13.89 9.21 4.59 −first order — — — — — — 77.35 63.60 54.66 47.37 diffraction light +first order 8.29 3.68 −0.90 −5.40 −10.13 −14.83 −19.62 −24.57 −29.72−35.15 diffraction light λ = 0.4 μm P = 0.61 μm (256 Mb)

TABLE 2 σ 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 Incidentangle ψ 53.13 46.05 39.79 34.06 28.69 23.58 18.66 13.89 9.21 4.59 −first order — — — — — — 77.35 63.60 54.66 47.37 diffraction light +first order 8.29 3.68 −0.90 −5.40 −10.13 −14.83 −19.62 −24.57 −29.72−35.15 diffraction light λ = 0.4 μm P = 0.61 μm (256 Mb)

TABLE 5 σ 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 Incidentangle ψ 53.13 46.05 39.79 34.06 28.69 23.58 18.66 13.89 9.21 4.59 −first order — — — — — — — — — 69.58 diffraction light + first order−3.28 −7.88 −12.54 −17.29 −22.16 −27.20 −32.49 −38.11 −44.20 −51.00diffraction light λ = 0.4 μm P = 0.7 μm (64 Mb)

Table 2 shows the values in a case that the wavelength λ is 0.4 μm andthe pattern pitch P is 0.61 μm, Table 3 shows the values in a case thatthe wavelength λ is 0.6 μm and the pattern pitch P is 0.61 μm, Table 4shows the values in a case that the wavelength λ is 0.4 μm and thepattern pitch P is 0.7 μm, and Table 5 shows the values in a case thatthe wavelength λ is 0.6 μm and the pattern pitch P is 0.7 μm, and theincident angle ψ and the diffraction angle θ are calculated according tothe above equations 1 and 2. In the LSI wafer pattern, the pattern pitchP=0.61 μm corresponds to 256 Mb and the pattern pitch P=0.7 μmcorresponds to 64 Mb. In the above tables, “−” denotes that calculationis impossible (the − first order diffraction light is not theoreticallygenerated). If the diffraction angle θ of the first order diffractionlight is 53.13 degrees or over, the first order diffraction light doesnot enter into the pupil 10 a of the objective lens 9 of NA=0.8.

A relationship between the annular-looped illumination (value σ=0.4,0.6) available with the above theoretical values and the + first orderdiffraction lights 25 and 25″ which are intensified and then obtainedfrom the grid pattern (FIG. 13 shows the pattern pitch P of 0.61 μm andFIG. 14 shows the pattern pitch P of 0.7 μm) is shown in FIGS. 13 and 14respectively.

FIG. 13 (a) shows the + first order diffraction light 25 which isintensified by the annular-looped illumination 24 of value σ=0.4, 0.6(wavelength λ shall be within the range of 0.4 to 0.6 μm) and obtainedfrom the grid pattern (corresponding to 256 Mb in the LSI wafer pattern)with the pattern pitch P of 0.61 μm, and FIG. 13(b) is a diagram showingthe range of the incident angle ψ of the annular-looped illumination 24with the value σ of 0.4, 0.6 (wavelength λ shall be within the range of0.4 to 0.6 μm) and the diffraction angle θ of the + first orderdiffraction light obtained from the grid pattern (corresponding to 256Mb in the LSI wafer pattern) with the pattern pitch P of 0.61 μm.

The diffraction range (range of diffraction angle θ) of the + firstorder diffraction light shown in FIG. 13(b) corresponds to theannular-looped illumination with the value σ of 0.4, 0.6 in Tables 2 and3. Intersecting oblique lines in FIG. 13(b) shows the area of the +first order diffraction light (corresponding to the area of the + firstorder diffraction light in a case that the average wavelength(wavelength λ is 0.5 μm) of the annular-looped illumination light) whichis obtained from the grid pattern with the pattern pitch P of 0.61 μm bybeing intensified with the annular-looped illumination with the value σof 0.4, 0.6. In other words, FIG. 13(a) shows an annular-looped area 25of the + first order diffraction light which is intensified and obtainedfrom the grid pattern with the pattern pitch P of 0.61 μm and enteredonto the pupil 10 a of the objective lens 9.

FIG. 14(a) shows the + first order diffraction light 25″ which isintensified by the annular-looped illumination 24 with the value σ of0.4, 0.6 (wavelength λ shall be within the range of 0.4 to 0.6 μm) andobtained from the grid pattern (corresponding to 64 Mb in the LSI waferpattern) with the pattern pitch P of 0.7 μm, and FIG. 14(b) is a diagramshowing the range of the incident angle ψ of the annular-loopedillumination 24 with the value σ of 0.4, 0.6 (wavelength λ shall bewithin the range of 0.4 to 0.6 μm) and the diffraction angle θ of the +first order diffraction light obtained from the grid pattern(corresponding to 64 Mb in the LSI wafer pattern) with the pattern pitchP of 0.7 μm.

The diffraction range (range of diffraction angle θ) of the + firstorder diffraction light shown in FIG. 14(b) corresponds to theannular-looped illumination with the value σ of 0.4, 0.6 in Tables 4 and5. Intersecting oblique lines in FIG. 14(b) shows the area of the +first order diffraction light (corresponding to the area of the + firstorder diffraction light in a case that the average wavelength(wavelength λ is 0.5 μm) of the annular-looped illumination light) whichis obtained from the grid pattern with the pattern pitch P of 0.7 μm bybeing intensified with the annular-looped illumination with the value σof 0.4, 0.6. In other words, FIG. 14(a) shows an annular-looped area 25″of the + first order diffraction light which is intensified and obtainedfrom the grid pattern with the pattern pitch P of 0.7 μm and enteredonto the pupil 10 a of the objective lens 9.

From comparison of FIGS. 13 and 14, it is apparent that, if the patternpitch P is smaller, the diffraction angle θ of the first orderdiffraction light becomes large and therefore the annular-loopedillumination is required.

Thus, the annular-looped illumination with the value σ of 0.4, 0.6 asshown in FIGS. 13 and 14 can be materialized by using the mask element 5b-6 shown in FIG. 4.

The above description is based on the equations 1 and 2 shown above. Inan experiment conducted by the present inventors, substantially the sameresults were obtained (the result shown in FIG. 13: the grid patternwith the pattern pitch P of 0.61 μm (corresponding to 256 Mb in the LSIwafer pattern); the result shown in FIG. 14: the grid pattern with thepattern pitch P of 0.7 μm) (corresponding to 64 Mb in the LSI waferpattern).

In the above-described embodiments shown in FIGS. 7 to 14, the gridpatterns which are repeated in the X axis direction in the LSI waferpattern as shown in FIG. 6 have been described. Actually, in the LSIwafer pattern, there is a grid pattern comprising pattern lines 102 tobe repeated in the Y axis direction as shown in FIG. 15.

The diffraction lights 22 a, 25 a and 26 a obtained from the gridpattern comprising pattern lines 102 repeated in the Y axis direction asshown in FIG. 15 with the annular-looped illumination 24 are enteredinto the pupil 10 a of the objective lens 9 as shown in FIG. 16. Thegrid pattern comprising pattern lines 101 shown in FIG. 6 and the gridpattern comprising pattern lines 102 shown in FIG. 15 are shifted by 90degrees from each other and therefore the state shown in FIG. 16 isobtained by rotating the state shown in FIG. 7 by 90 degrees.

Accordingly, the state of generation of the diffraction light obtainedfrom the grid pattern comprising the pattern lines 102 shown in FIG. 15is the same as obtained by rotating the state of generation of thediffraction light shown in FIGS. 8 to 10 by 90 degrees. In other words,it is apparent that the 0th order diffraction light 22 a, + first orderdiffraction light 25 a and − first order diffraction light 26 a obtainedreflected at the grid pattern shown in FIG. 15 from the incidentillumination light 24 a entered into the Y-Z plane passing through theoptical axis 33 of the incident annular-looped illumination light 24,are made incident onto the pupil 10 a of the objective lens 9 as shownin FIG. 16 and the incident illumination light 24 a in a directionintersecting the pattern lines 102 is effective for improvement of theresolution.

However, even though the + first order diffraction light 25 b and the −first order diffraction light 26 b, which are obtained from reflectionof the incident illumination light, which is made incident into the X-Zplane passing through the optical axis 33, of the incidentannular-looped illumination light 24 from the grid pattern shown in FIG.15, are introduced into the pupil 10 a of the objective lens 9 asdescribed in FIG. 9, such diffraction lights are weaker than the 0thorder diffraction light 22 b and do not contribute to improvement of theresolution and therefore it is preferable to eliminate the incidentillumination light to be made incident in the X axis direction (X-Zplane passing through the optical axis 33) of the incidentannular-looped illumination light 24 by using the mask element 5 a-mshown in FIG. 3.

In any event, the CPU 20 can detect the distribution of the incidentdiffraction light which is produced from the grid pattern and enteredinto the pupil 10 a of the objective lens 9 by the annular-loopedillumination, according to the image signals obtained from the imagesensor 12 b which receives the image (the producing position andbrightness of the 0th order diffraction light 22 a and the producingposition and brightness of the + first order diffraction light 25 a) onthe pupil 10 a (Fourier transform plane) of the objective lens 9.

In other words, the CPU 20 can select the mask element by driving andcontrolling the moving mechanism 19 in accordance with the distribution(the producing position and brightness of the 0th order diffractionlight and the producing position and brightness of the + first orderdiffraction light 25 a) of the diffraction light to be entered into thepupil 10 a of the objective lens 9 detected according to the imagesignals to be obtained from the image sensor 12 b, and can obtain anannular-looped illumination suitable for the grid pattern (LSI waferpattern) of the inspected object 1. Consequently, high resolution imagesignals of the grid pattern (LSI wafer pattern) of the inspected object1 can be obtained from the image sensor 12 a.

The following describes the operation of a device as represented, forexample, by the attenuation filter 38 for partly controlling theintensity of light which is provided at a position 10 b in conjunctionwith the position of the pupil 10 a of the objective lens 9.Specifically, as shown in FIGS. 9 and 10, the 0th order diffractionlight 22 b′, 22 b′ which need not be entered into the pupil 10 a of theobjective lens 9 and received by the image sensor 12 a can be shut offby the attenuation filter 38. In this case, the attenuation filter 38serves as a space filter.

By controlling the intensity of the 0th order diffraction light 22 aentered into the pupil 10 a of the objective lens 9 as shown in FIGS. 8and 16 by the attenuation filter 38 provided at the position 10 b inconjunction with the position of the pupil 10 a of the objective lens 9as shown in FIGS. 17 and 18, the image sensor 12 a is able to balancethe intensity of the 0th order diffraction light 22 a and the intensityof the + first order diffraction light 25 a which are entered into thepupil 10 a of the objective lens 9 and receive these diffraction lightsand consequently, the image of the grid pattern of the inspected object1 can be detected with high resolution and high contrast. Theabove-described attenuation filter 38 has a shape identical to the maskelement shown in FIG. 3. However, as shown in FIG. 3, the attenuationfilter 38 need not have a ring type shape and can be shaped as desiredif it is able to control the light intensity at a desired position.However, if a ring-shaped attenuation filter 38 is used, it is necessaryto optimize the annular-looped illumination 24 so that the 0th orderdiffraction light 22 a and the + first order diffraction light 25 a arenot generated in the same ring-shaped area.

FIG. 17 is a diagram showing that the 0th order diffraction light 22 aand the + first order diffraction light 25 a generated from the gridpattern of the inspected object 1 by the annular-looped illumination 24a reaches the pupil 10 a of the objective lens 9 and the pupil 10 b at aposition in conjugation with the pupil 10 a. FIG. 18 is a diagramshowing the attenuation filter 38 disposed on the pupil 10 b. In otherwords, it is known that, of the 0th order diffraction light 22 a andthe + first order diffraction light 25 a which are introduced into thepupil 10 a of the objective lens 9, the intensity of the 0th orderdiffraction light 22 a is controlled on the pupil 10 a by theattenuation filter 38.

FIG. 19(a) is a schematic diagram of an attenuation filter 38 a showingthe transmission characteristic of the attenuation filter 38 a and FIG.19(b) shows a graphical shape thereof. FIG. 20(a) shows anotherattenuation filter 38 b and the transmission characteristic thereof andFIG. 20(b) shows a graphical shape thereof. The transmissioncharacteristic of the attenuation filter 38 and the graphical shapethereof can be optimized in compliance with the 0th order diffractionlight 22 a and the + first order diffraction light 25 a which areproduced from the grid pattern of the inspected object 1 by theannular-looped illumination 24 a.

If the annular-looped illumination can be optimized in accordance withthe grid pattern (LSI wafer pattern) of the inspected object 1, theattenuation filter 38 need not be provided. However, for optimizationonly with the annular-looped illumination, it is necessary to prepareand select various types of annular-looped illuminations to meet varioustypes of patterns on the inspected object 1. For minimizing the scope ofselection of the annular-looped illumination, it is preferable tocontrol the intensities of the diffraction lights by using theattenuation filter 38 at the light receiving side and detect the imageof the grid pattern of the inspected object 1 in high resolution andcontrast by the image sensor 12 a.

The CPU 20 can select the attenuation filter 38 by driving andcontrolling the moving mechanism 39 in accordance with the distributionsof the diffraction lights (the producing position and brightness of the0th order diffraction light 22 a and the producing position andbrightness of the + first order diffraction light 25 a) which aredetected according to the image signals obtained from the image sensor12 b and entered into the pupil 10 a of the objective lens 9, and canobtain the intensities of the 0th order diffraction light and the +first order diffraction light suited to the grid pattern (LSI waferpattern) of the inspected object 1. Consequently, high resolution imagesignals of the grid pattern (LSI wafer pattern) of the inspected object1 can be obtained from the image sensor 12 a.

Since it is difficult to implement optimization only with theannular-looped illumination to meet various patterns on the inspectedobject 1, it is necessary to control the intensities of the diffractionlights received by the image sensor 12 a through the attenuation filter38 as described above, and the detection sensitivity by controlling thethreshold values in image processing to be carried out by the comparatorcircuit 17 or the CPU 20 . The control of the threshold values in imageprocessing to be carried out by the comparator circuit 17 or the CPU 20can be carried out according to the image on the pupil 10 b of theobjective lens 9 to be detected by the image sensor 12 b or the image ofthe pattern on the inspected object 1 to be detected by the image sensor12 a.

The CPU 20 can be adapted to determine an area having a pattern withhigh repeatability such as, for example, a memory cell in accordancewith a locality distribution (the producing position and the intensityincluding the spread) of the diffraction light in the image (image onthe pupil 10 b of the objective lens 9) on the Fourier transform planeto be detected by the image sensor 12 b, and to control the thresholdvalues in image processing to be carried out by the comparator circuit17 or the CPU 20, to raise the detection sensitivity. On the contrary,in a case that the CPU 20 determines an area having a pattern with alower repeatability, the detection sensitivity can be lowered bycontrolling the threshold values in image processing to be carried outby the comparator circuit 17 or the CPU 20.

Particularly, for inspecting a defect of a pattern on the inspectedobject 1 in image processing to be carried out by the comparator circuit17 or the CPU 20, a defect in an area including a pattern having highrepeatability such as, for example, a memory cell can be easily detectedwith the annular-looped illumination, by controlling the thresholdvalues to increase the detection sensitivity in accordance with thelocality distribution (the producing position and the intensityincluding the spread) of the diffraction light in the image (the imageon the pupil 10 b of the objective lens 9) on the Fourier transformplane to be detected by the image sensor 12 b.

Another embodiment in which the shape of the ring of the annular-loopedillumination to be emitted from the disc type mask (secondary lightsource for annular-looped illumination) formed with a plurality ofvirtual spot light sources is changed is described with reference toFIGS. 21 and 22. In other words, FIGS. 21 and 22 show other embodimentsfor controlling various annular-looped illuminations. In FIG. 21, theshape of the ring is changed and the annular-looped illumination iscontrolled by moving the light house 124 comprising the Xe lamp 3, theelliptic mirror 4 and the disc type mask 5 for forming theannular-looped illumination towards the collimator lens 6 in the opticalaxis direction. In FIG. 22, the shape of the ring is changed and theannular-looped illumination is controlled by moving the collimator lens6 toward the light house 124 comprising the Xe lamp 3, the ellipticmirror 4 and the disc type mask 5 for forming the annular-loopedillumination in the optical axis direction.

In an embodiment of the light house 124 which forms the secondary lightsource 5 for the annular-looped illumination formed with a plurality ofvirtual spot light sources shown in FIGS. 1, 21 and 22, an arrangementof the Xe lamp 3 in the vertical direction is shown. When the Xe lamp 3is arranged in the vertical direction, the light flux in the opticalaxis direction reduces and therefore the Xe lamp can be arranged in thehorizontal direction to increase the light flux in the optical axisdirection. Not only the Xe lamp but also a Hg lamp and a halogen lampcan be used as the light source in the light house 124.

In a case that the disc type mask 5 (secondary light source forannular-looped illumination) formed with a plurality of virtual spotlight sources is selected in accordance with the pattern of theinspected object 1, the light quantity of the annular-loopedillumination emitted from the secondary light source 5 for theannular-looped illumination substantially varies and the CPU 20 controlsthe light quantity by controlling the light quantity adjusting filter 14such as an ND filter in accordance with an image signal 41 obtained fromthe image sensor 12 a through the A/D converter 19.

A microscope system (microscopic observation system) to be used ininspection of a pattern of an inspected object 1 using an annular-loopedillumination according to the present invention is described withreference to FIG. 23 which shows a microscope system (microscopicobservation system) according to a second embodiment of the presentinvention applied to the inspection of the pattern of the inspectedobject 1 such as an LSI wafer pattern (microscopic observation system)according to the second embodiment of the present invention.

The microscope system using the annular-looped illumination formed witha plurality of virtual spot light sources is described only with respectto its characteristic parts with omission of the description of theparts common to the pattern inspection apparatus shown in FIG. 1. InFIG. 23, members 12 a′ and 12 b′ represent TV cameras which are used asthe image sensors 12 a and 12 b shown in FIG. 1 and the operator canvisually observe the output images from the TV cameras on monitors 27 aand 27 b. Members 12 a′ and 12 b′ can be used if they can detect theimage, and can therefore be formed with image sensors and not the TVcameras.

In other words, the TV camera 12 a′ detects a pattern image and the TVcamera 12 b′ detects an image on a pupil 10 a of an objective lens 9,and these images are displayed on the monitors 27 a and 27 b. Acontroller 46 is connected to a specimen stage 2 so as to be driven andcontrolled for movement in X, Y, Z and θ (rotation) axis directions by adriver 45. This controller 46 drives and controls the moving mechanism19, the light house 124, and the collimator lens 6 in accordance with animage with a locality distribution of the first order diffraction lightincluding the 0th order diffraction light which are introduced into thepupil 10 a of the objective lens 9 and detected by the TV camera 12 b′and displayed on the monitor 27 b, and selects the annular-loopedillumination or a normal circular illumination suited for the pattern ofthe inspected object 1. For driving and controlling the disc type mask 5by the moving mechanism 19, a mask element formed on the disc type mask5 can be selected. For driving and controlling the light house 124 andthe collimator lens 6, these can be driven and controlled relatively inthe arrow direction as shown in FIGS. 21 and 22.

The controller 46 drives and controls the moving mechanism 39 andselects an attenuation filter 38 suited for the pattern of the inspectedobject 1 according to an image of a locality distribution of the firstorder diffraction light including the 0th order diffraction light whichare entered into the pupil 10 a of the objective lens 9 and detected bythe TV camera 12 b′ displayed on the monitor 27 b. If a circularillumination suitable or normal for the pattern of the inspected object1 can be selected with the secondary light source 5 for theannular-looped illumination, the attenuation filter 38 need not alwaysbe provided.

The controller 46 controls the light quantity control filter 14 toobtain an appropriate quantity of light from the pattern of theinspected object 1 by driving and controlling a control mechanism 14 baccording to an image of the pattern of the inspected object 1 which isdetected by the TV camera 12 a′ and displayed on the monitor 27 a.

A microscopic observation system thus using the annular-loopedillumination enables to observe a high density pattern with highresolution and contrast according to the image of the pattern of theinspected object 1, which is detected by the TV camera 12 a′ anddisplayed on the monitor 27 a, even though the pitch P (for example, 0.7μm or 0.61 μm) of the grid pattern such as memory devices as 64 Mb DRAMand 256 Mb DRAM as on the LSI wafer pattern is close to wavelength λ(for example, 400 to 600 nm) of the illumination light to result in thehigh density.

When a mask element with the value σ of approximately 0.5 is used forillumination in the annular-looped illumination, an image of deep grooveor hole can be received by the TV camera 12 a′ and displayed with highcontrast on the monitor 27 a.

Modifications of the above-described first and second embodiments as athird embodiment are now described. The above-described first and secondembodiments have been described with respect to the annular-loopedillumination and the circular illumination. The above-describedannular-looped illumination includes a modified illumination (slantedillumination) (This modified illumination is based on the illuminatingcondition under which at least the 0th order diffraction light and thefirst order or second order diffraction light are introduced into thepupil 10 a of the objective lens 9.). The dark field illumination is notincluded in the modified illumination (slanted illumination) since the0th order diffraction light thereof is not generally entered into thepupil 10 a of the objective lens 9.

In the first and second embodiments, the transmissivity of light isattenuated by the attenuation filter 38 as shown in FIGS. 19 and 20.However, the light quantity of the 0th order diffraction light 22 a canbe attenuated as compared with the + first order diffraction light 25 areceived by the image sensor 12 a by a phase shifting method, that is, amethod for shifting the phase of the 0th order diffraction light 22 a byusing a phase film. In other words, although a device such as theattenuation filter 38 for partly controlling the light intensity isprovided at a position 10 b in conjugation with the position of thepupil 10 a of the objective lens 9 in the first and second embodiments,a phase plate can be provided at this position 10 b. For example, theintensity of the 0th order diffraction light 22 a received by the imagesensor 12 b can be attenuated by advancing the phase of the 0th orderdiffraction light 22 a as much as π/2 with reference to the phase ofthe + first order diffraction light 25 a. In addition, the intensity ofthe 0th order diffraction light 22 a to be received by the image sensor12 b can be attenuated by providing the phase plate with an absorptioncharacteristic.

Although, in the first and second embodiments, the 0th order diffractionlight and ± first order diffraction lights are described in acombination framework, it is apparent that these embodiments can applyto the framework of the 0th order diffraction light (non-diffractionlight) and the diffraction light (± first order diffraction lights and ±second order diffraction lights). In other words, the annular-loopedillumination can be used so that the 0th order diffraction light andthe + second order diffraction light or the − second order diffractionlight obtained from the pattern are made incident into the pupil 10 a ofthe objective lens 9, even though the pitch P of the pattern becomesfiner (the pattern has a higher density). Generally, the first orderdiffraction angle is smaller than the second order diffraction angle asgiven in the relationship represented by the equation 2. However, insome cases, the second order diffraction angle may be smaller than thefirst order diffraction angle depending on the pitch P of the patternand the wavelength λ of the annular-looped illumination.

In the first and second embodiments, for example, the Xe lamp 3 (thedimensions are not shown) is used as the light source in the light house124 but a large light source (a light source which irradiates anincoherent light) or a spot light source (a light source whichirradiates a coherent light) can be used. An appropriate value σ can beobtained only with the primary light source (without a mask element) byselecting the light source.

Although the first and second embodiments are described with a commonwavelength of 400 to 600 nm as the wavelength λ of the annular-loopedillumination, the illumination wavelength is not described. A wavelengthof the so-called i ray (approximately 365 nm) or a short wavelength ofan excimer laser beam (ultraviolet ray) can be used as the wavelength λof the annular-looped illumination. It is apparent that the resolutioncan be further improved if a light of short wavelength such as theexcimer laser beam (ultraviolet ray) is used.

The control of the annular-looped illumination in the first and secondembodiments can be carried out for each type of pattern of the inspectedobject (for example, in case of the LSI wafer pattern, each process oreach type of the LSI wafer ). The annular-looped illumination can bedynamically controlled in one LSI wafer. In case of inspecting a defectof the pattern of the inspected object 1, the sensitivity can becontrolled for each type of pattern of the inspected object as in thecontrol of the annular-looped illumination or can be dynamicallycontrolled in one LSI wafer.

The secondary light source for the annular-looped illumination,including the primary light source (Xe lamp 3) for use in the lighthouse 124 in the first and second embodiments can be adjusted by using amirror surface wafer as the inspected object 1 so that a ring typeintensity distribution (a distribution of a ring-shaped 0th orderdiffraction light 22 on the pupil 10 a of the objective lens 9 to bedetected by the image sensor 12 b) becomes uniform. In other words, thesecondary light source for the annular-looped illumination can beadjusted by adjusting, for example, the positions of the Xe lamp 3 andan elliptic mirror 4 which forms the secondary light source for theannular-looped illumination so that the distribution of the ring-shaped0th order diffraction light 22 on the pupil 10 a of the objective lens 9detected by the image sensor 12 b using the mirror surface wafer as theinspected object 1.

In the first and second embodiments, it is described that the imageinformation (monitor information) based on the locality distribution(position and brightness, including the spread) of the diffractionlights (0th order diffraction light and + first order diffraction light)on the pupil 10 a of the objective lens 9 detected by the image sensors12 b and 12 b′ is used to control various parts by the CPU 20 or thecontroller 46. In other words, the control of the conditions for variousparts includes the control of illumination conditions such as control ofthe annular-looped illumination (for example, control of IN σ and OUT σand the incident range shown in FIGS. 3 and 4) and the light quantitycontrol by means of the light quantity control filter 14, the control ofthe light quantity detected by the attenuation filter 38, and thecontrol of detection sensitivity in the comparator circuit 17. The CPU20 or the controller 46 determines whether the image information basedon the locality distribution of the is diffraction lights on the pupil10 a of the objective lens 9 detected by the image sensors 12 b and 12b′ is obtained, for example, from the repeated portion or the other areaof the memory device and consequently, can controls the annular-loopedillumination including an appropriate circular illumination inaccordance with whether the identified repeated portion or the otherportion.

A fourth embodiment of the present invention for inspecting a defect ofa memory cell part of an LSI wafer pattern by using an annular-loopedillumination to improve the optical resolution is described withreference to FIGS. 24 to 27. FIG. 24 shows a defect of the memory cellpart of the LSI wafer pattern. FIG. 25 shows the relationship betweenthe LSI wafer pattern and the detection pixel obtained from an A/Dconverter 15 a. FIGS. 26(a) and 26(b) show a pattern and a waveform ofan image signal received with high resolution from a high densitypattern by the image sensor 12 a with the annular-looped illuminationand obtained from the image sensor 12 a. FIGS. 27(a) and 27(b) explainsampling of image signals shown in FIG. 26 to be carried out by the A/Dconverter 15 a.

There are various defects (for example, a projection 231, an opening232, a discoloration 233, a short-circuiting 234, a chipping 235, and astain 236) on the memory cell part of the LSI wafer pattern as shown inFIG. 24 and therefore, for detecting these defects with highreliability, the inspection apparatus should be able to detect the LSIwafer pattern as image signals with high resolution by the image sensor12 a. High resolution image signals shown in FIG. 26(b) are obtainedfrom the pattern shown in FIG. 26(a) by using the annular-loopedillumination. FIG. 26(a) shows a partly extended view of the patternshown in FIG. 24 and FIG. 26(b) shows the waveform indicating theposition of the pattern A-A′ on the horizontal axis and the brightnessof the image signal (pattern detection signal) obtained from the imagesensor on the vertical axis. In FIG. 26(a), it is shown that highresolution image signals representing the edge information of thepattern are obtained from the image sensor 12 a by using theannular-looped illumination.

When the annular-looped illumination is used, the +first orderdiffraction light with various diffraction angles and a spread (dullspread) is obtained from the defects such as the projection 231, thechipping 236 and the stain 235 and image signals differing from thepattern can be obtained from the image sensor 12 a. When theannular-looped illumination is used, the image signals including thoseof the opening 232 and the short-circuiting 234, differing from thepattern can be obtained from the image sensor 12 a since the + firstorder diffraction light component in the X axis direction is notgenerated. When the annular-looped illumination is used, generation of,for example, the 0th order diffraction light from the discolorationdefect 233 differs from that from an area where there is nodiscoloration defect, and the image signal showing the discolorationdefect 233 can be obtained from the image sensor 12 a.

FIG. 25 shows a case that the detection pixel to be sampled in the A/Dconverter 15 a with respect to the LSI wafer pattern shown in FIG. 24 islarge. In the case that the detection pixel 241 to be sampled in the A/Dconverter 15 a is large as shown in FIG. 25, two edges of the patternremain in one detection pixel 241 and the edge information of thepattern will be lost.

To prevent loss of the edge information of the pattern, the dimensionsof the detection pixel 241 to be sampled in the A/D converter 15 a canbe reduced. When the dimensions of the detection pixel are reduced,sampled digital image signal information obtained from the A/D converter15 a increases, a volume of defect detection image signal information tobe processed in the comparator circuit 17 also increases and thereforeit takes a lot of time to detect the defect. Accordingly, as shown inFIG. 27, the pattern A-A′ can be sampled in a detection pixel size thatthe minimum and maximum values of brightness of the pattern arepreserved, and converted to the digital image signals showing the shade(brightness).

The CPU 20 calculates an interval between the minimum value (edgeinformation of the pattern) and the maximum value of the brightness ofthe pattern from a digital image signal 41 (shown in FIG. 27(a))obtained from the A/D converter 15 a by reducing the pixel size to besampled by the A/D converter 15 a, and sets a detection pixel size bywhich these minimum and maximum values can be divided. The A/D converter15 a carries out sampling according to the detection pixel size 42 setin the CPU 20 and therefore the digital image signal (shown in FIG.27(b)) showing the shade (brightness) which is sampled in a relativelylarge detection pixel size can be obtained without losing the edgeinformation of the pattern. Consequently, the volume of information forprocessing the defect detection image to be carried out in thecomparator circuit 17 and others can be reduced and the defect can bedetected in high speed and reliability.

Referring to FIG. 27(a), the CPU 20 sets the pixel size to be sampled tobe small for the A/D converter 15 a, selects X1/2 as the detection pixelsize among X1, X2, X3 and X4 portions which have the relation ofX1=X2=X3=X4 from the digital image signal 41 obtained from the A/Dconverter 15 a, and sets X5 and X6 portions where the interval betweenthe minimum value and the maximum value is large so that the detectionpixel size is 3X₁/2 and 2X₁. A signal 42 corresponding to the detectionpixel size which is set as described above is supplied to the A/Dconverter 15 a.

FIG. 27(b) shows a waveform of a digital image signal sampled in the A/Dconverter 15 a according to the signal 42 supplied from the CPU 20 forthe waveform of the image signal of A-A′ part shown in FIG. 27(a). Asknown from FIG. 27 (b), in the A/D converter 15 a, the digital imagesignals which contain the minimum and maximum values showing the patternedge are obtained from the image signals outputted from the image sensor12 a. With this, the image signals showing the pattern edge to beobtained in high resolution are erased and a defect can be inspectedwith high reliability at a high speed by cell-comparing orchip-comparing digital image signals which are delayed as far as thecell interval or the chip interval in the delay memory 16 and thedigital image signals directly obtained from the A/D converter 15 a. Theimage signals indicating the pattern edge are repeated at the cellinterval or the chip interval and simultaneously detected in cellcomparison or chip comparison in the comparator circuit 17 and the imagesignal indicating the pattern edge can be erased. Consequently, a signal18 indicating a defect can be detected unmatched in cell or chipcomparison in the comparator circuit 17.

The CPU 20 can set the detection pixel size to X=X₁/4 or X₁/8 to carryout sampling of digital image signals between the minimum value and themaximum value. Thus, the A/D converter 15 a can obtain the digital imagesignals showing the shade (brightness) from sampling in the above setdetection pixel size (X=X₁/4 or X₁/8). In this case, the samplinginterval is reduced and therefore high resolution image signals obtainedfrom the image sensor 12 a can be faithfully converted to the digitalimage signals.

The CPU 20 can vary the magnification of the image received by the imagesensor 12 a according to the digital image signal 41, which is obtainedfrom the A/D converter 15 a by reducing the pixel size to be sampled forthe A/D converter 15 a, by controlling the zoom lens 13 with a zoom lenscontrol signal 43 as shown in FIG. 1. Consequently, even though thesignal 42 for determining the detection pixel size is fixed in the A/Dconverter 15 a, the detection pixel size to be sampled can be varied inaccordance with the magnification depending on the zoom lens 13.Accordingly, for varying the magnification depending on the zoom lens13, the zoom lens can be controlled with a command from the CPU 20.

In addition, sampling of high resolution image signals obtained byreceiving the 0th order diffraction light 22 a and the + first orderdiffraction light 25 a, which are generated from the grid pattern by theannular-looped illumination and entered into the pupil 10 a of theobjective lens 9, in the A/D converter 15 a is described with referenceto FIGS. 28, 29 and 30. The grid pattern (wafer pattern formed withlines and spaces) respectively shown in FIGS. 28(a) to 30(a) is arepetitive pattern comprising lines of 0.42 μm in width and spaces of0.42 μm in width which are repeated at the pitch P of 0.84 μm.

The waveform of the sampled digital image signal showing the shade(brightness) shown in FIG. 28(b) is obtained when the detection pixelsize is set to 0.0175 μm and it is known that the edge information ofthe grid pattern is clearly detected. In other words, it is indicatedthat high resolution image signals obtained by being received by theimage sensor 12 a are faithfully converted to the digital image signalindicating the shade (brightness) by the A/D converter 15 a.

The waveform of the sampled digital image signal showing the shade(brightness) shown in FIG. 29(b) is obtained when the detection pixelsize is set to 0.14 μm and it is known that the edge information(information of ultimate values such as minimum and maximum values) ofthe grid pattern is detected as being stored.

The waveform of the sampled digital image signal showing the shade(brightness) shown in FIG. 30(b) is obtained when the detection pixelsize is set to 0.28 μm and it is known that the edge information(information of ultimate values such as minimum and maximum values) ofthe grid pattern is detected as being partly missed.

Therefore, the repetitive pattern (grid pattern) comprising lines of0.42 μm in width and spaces of 0.42 μm in width which are repeated atthe pitch P of 0.84 μm should be converted to the digital image signalindicating the shade (brightness) by sampling in the A/D converter 15 awhile setting the detection pixel size to be set according to the signal42 from the CPU 20 to approximately 0.3 μm or less. With this, the edgeinformation (information of ultimate values such as minimum and maximumvalues) of the grid pattern is detected as being stored in the digitalimage signal showing the shade (brightness) and can be detected as beingdiscriminated from the defect and therefore those defects (projection231, opening 232, discoloration 233, short circuiting 234, chipping 235and stain 236, etc.) can be detected through cell comparison or chipcomparison in the comparator circuit 17.

When sampling in which the minimum and maximum values of to the patternare preserved is executed in the A/D converter 15 a, the patterninformation is not damaged even in case of a large detection pixel sizeand high precision defect inspection can be carried out at a high speedin the comparator circuit 17.

In the embodiments shown in FIGS. 28 to 30, the waveform of the sampleddigital image signal indicating the shade (brightness) is described witha one-dimensional grid pattern and it is apparent that these embodimentscan also apply to a two-dimensional grid pattern.

The above-described embodiments include the embodiment for inspecting adefect on the pattern formed on the inspected object 1 and theembodiment of the microscopic observation system for observing thepattern formed on the inspected object 1. The present invention canapply as a fifth embodiment to inspection of impurities which remain onthe pattern formed on the inspected object 1 and measurement of thedimensions of the pattern formed on the inspected object 1.

As described in the fourth embodiment, for example, the CPU 20 canmeasure the dimensions of the pattern with high accuracy. Impuritieswhich exist on the pattern (LSI wafer pattern) formed on the inspectedobject 1 can be detected as in inspection of defects. In other words,the first order or higher order diffraction lights which have variousdiffraction angles are introduced from impurities into the pupil 10 a ofthe objective lens 9 as in the case of projection defect 231 (FIGS.24-25) and chipping defect 236 (FIGS. 24-25). On the other hand, the 0thorder diffraction light and the + first order diffraction light from thepattern are entered into the pupil 10 a of the objective lens 9,different image signals are detected from the image sensor 12 a, andimpurities can be detected by cell comparison or chip comparisonexecuted in the comparator circuit 17. Those impurities on a mirrorsurface wafer can be similarly detected.

As described in the following embodiments, the information of thepattern can be erased by using a space filter 309 not erased by cellcomparison or chip comparison. Impurities can be detected according tothe image signals on the pupil 10 a of the objective lens 9 which aredetected by the image sensor 12 b. In other words, the impurities on themirror surface wafer can be directly detected from the image signals onthe pupil 10 a of the objective lens 9 detected by the image sensor 12b. Impurities which exist on the pattern (LSI wafer pattern) formed onthe inspected object 1 can be detected by erasing the patterninformation from the image signals on the pupil 10 a of the objectivelens 9 detected by the image sensor 12 b, since the localitydistribution of the diffraction lights entering into the pupil 10 a ofthe objective lens 9 is different between the impurities and thepattern.

Specifically, the impurities can be detected by storing the referenceimage signals on the pupil 10 a obtained from a normal pattern on whichno impurities exist and which is detected by the image sensor 12 b inthe delay memory 16, and comparing the stored reference image signals onthe pupil 10 a and the image signals on the pupil 10 a obtained from theinspected pattern to be actually detected by the image sensor 12 b toerase the pattern information. The pattern information can be erased andthe impurities can be detected by masking (shielding) the localitydistribution information of the diffraction lights on the pupil 10 a tobe obtained from the inspected pattern with the locality distributioninformation or the reversed locality distribution information (spacefilter 309 in FIGS. 31 and 33) of the diffraction lights on the pupil 10a to be obtained from the normal pattern.

A practical configuration of an optical system for use in the patterninspection apparatus according to the present invention as a sixthembodiment is described with reference to FIGS. 31 and 32, whichrespectively show the practical configuration of the optical system tobe used in the pattern inspection apparatus shown in FIG. 1, whereinFIG. 31 is a plan view and FIG. 32 is a front view thereof.

The configuration of the optical system shown in FIGS. 31 and 32 for usein the pattern inspection apparatus is basically the same as theconfiguration of the optical system shown in FIG. 1 for the patterninspection apparatus. In this embodiment, a television camera TV₁ forannular-looped illumination (bright field illumination) and a televisioncamera TV₂ for dark field illumination as TV cameras for observingimages, and a television camera TV₄ for dark field illumination as a TVcamera for observing the pupil 10 a of the objective lens 9 are added.Accordingly, the TV camera TV₁ for annular-looped illumination (brightfield illumination) and the TV camera TV₂ for dark field illuminationare used to observe the images. The TV camera TV₃ for annular-loopedillumination (bright field illumination) to be used as the TV camera forobserving the pupil 10 a of the objective lens 9 is the same as theimage sensor 12 b.

Specifically, based on an image (a locality distribution of thediffraction light obtained from the pattern on the inspected object 1with annular-looped illumination) on the pupil 10 a to be picked up bythe TV camera TV₃ (12 b) for annular-looped illumination (bright fieldillumination), the CPU 20 selectively controls a defect detectionsensitivity in the filter (disc type mask: opening diaphragm) 5 forannular-looped illumination, the pupil filter (attenuation filter) 38for controlling the light quantity of the 0th diffraction light or thecomparator circuit 17; a detection pixel size to be obtained fromsampling by the A/D converter 15 a; or a magnification depending on thezoom lens 13. Based on the image (a distribution of scattering light tobe obtained from the pattern on the inspected object 1 with dark fieldillumination described later) on the pupil 10 a to be picked up by theTV camera TV₄ for dark field illumination, the CPU 20 selectivelycontrols an impurity detection sensitivity in the space filter 309 orthe comparator circuit, or the detection pixel size to be obtained fromsampling by the A/D converter for A/D-converting the image signalsobtained from a linear image sensor 308. Thus, the microscopicobservation system can be adapted for the pattern on the inspectedobject 1.

A dichroic mirror 325 admits to pass a light of the image on the pupil10 a as the diffraction light to be obtained from the inspected object 1with the annular-looped illumination of 600 nm or under in wavelength,and reflects a light of the image on the pupil 10 a as the scatteringlight to be obtained from the inspected object 1 with the dark fieldillumination of 780 to 800 nm in wavelength, which is described later.Reference numerals 326 is a mirror.

The light house 124′ comprises two types of lamps, that is, a Hg-Xe lampL₁ and a Xe lamp L₂ as the primary light sources 3 and 4 shown in FIG. 1and these two types of the primary light sources are adapted to bechanged over by a mirror 317 for changeover. The Hg-Xe lamp L₁ has abrightness spectrum and is available for high intensity illuminationwith a width of short wavelength and the Xe lamp L₂ can provideincandescent illumination. In other words, for annular-loopedillumination including circular illumination through the filter 5 forannular-looped illumination (secondary light source for annular-loopedillumination: disc type mask: opening diaphragm), the illumination canbe made by changing over high intensity illumination at the width ofshort wavelength using the Hg-Xe lamp L₁ and incandescent illuminationusing the Xe lamp L₂.

An integrator 318 as shown in FIG. 33, is provided for making uniformthe intensity of light emitted from the Hg-Xe lamp L₁ or the Xe lamp L₂and an intensity monitor 341 is provided for monitoring variations ofthe intensity of light in the primary light sources L₁ and L₂. The lightquantity control filter 14 is controlled and the conversion level in theA/D converter 15 is compensated, in accordance with the variations ofthe intensity in the primary light sources L₁ and L₂ monitored by anintensity monitor 341, as shown in FIG. 33. A wavelength selectionfilter 316 is provided for selecting the wavelength of theannular-looped illumination light to, for example, 600 nm or under. Afield diaphragm 319 is provided for shielding a light other than theannular-looped illumination and a mirror 301 is also provided.

A dichroic mirror 320 provided in the front of a second objective lens303 is intended to pass the diffraction light obtained from theinspected object 1 with the annular-looped illumination of wavelength of600 nm or under, and reflect a scattering light obtained from theinspected object 1 with the dark field illumination of wavelength of 780to 800 nm described later. There is also provided a half mirror 321 andlenses 326 a and 326 b. A space image formed with a scattering lightproduced from the pattern on the inspected object 1 with the dark fieldillumination of wavelength of 780 to 800 nm is formed at the position ofthe space filter 309. Further, there is provided mirrors 322, 324 and327 and a half mirror 323, as shown in FIG. 33.

In addition, a dark field illumination optical system (304, 305, 306 and307) for focusing a laser beam emitted from a semiconductor laser beamsource L₃ and slantly irradiating the laser beam onto the inspectedobject 1 (LSI wafer) is provided so that the impurities can be detectedwith high sensitivity. A beam expander 304 (beam expanding opticalsystem) is provided for the diameter of the laser beam emitted from thesemiconductor laser beam source L₃ and mirrors 305 and 306 are providedfor reflecting the laser beam while a focusing lens 307 is provided forfocusing the laser beam the diameter of which is expanded and slantlyirradiating the laser beam onto the inspected object 1.

The 0th order diffraction light (positive reflection light) producedfrom the inspected object 1 with dark field illumination by the darkfield illumination optical system (304, 305, 306 and 307) is not enteredinto the pupil 10 a of the objective lens 9 and only the scatteringlight (first order or higher order diffraction light) produced fromimpurities on the inspected object 1 is entered into the pupil 10 a ofthe objective lens 9 and received by the image sensor 308, which outputsthe signals to enable detection of the impurities. A space filter 309 isprovided which shuts off to erase the scattering light (first order orhigher order diffraction light) which is produced from the pattern edgeon the inspected object 1 with the dark field illumination and enteredinto the pupil 10 a of the objective lens 9. The wavelength of the laserbeam emitted from the semiconductor laser beam source L₃ is an optionalwavelength, for example, 780 to 800 nm, different from the wavelength ofthe annular-looped illumination (bright field illumination) from thelight house 124′.

In addition, an automatic focus control optical system is provided todetect the pattern on the inspected object 1 with high accuracy as theimage signals by the image sensor 12 a. This automatic focus controloptical system comprises a light source 310, a filter 313 for obtaininga wavelength of 600 to 700 nm, a pattern 315 for automatic focus (A/F),a projector lens 314 for projecting the pattern 315 for A/F on theinspected object 1, half mirrors 312 and 313, and sensors S₁ and S₂arranged in the front and back of focusing plane.

The surface (pattern surface) of the inspected object 1 is focused withthe objective lens (imaging optical system) 9 by slightly controllingthe inspected object 1 in the vertical direction as shown with an arrowmark so that the contrast signals of the A/F pattern 315, which isprojected onto the inspected object 1 by the projector lens 314, arerespectively detected by the sensors S₁ and S₂, and the contrast signalobtained from the sensor S₁ coincides with the contrast signal obtainedfrom the sensor S₂. The dichroic mirror 302 provided in the light pathof the detection optical system reflects a light of 600 to 700 nm inwavelength for automatic focusing and admits to pass a light of 600 nmor under in wavelength for annular-looped illumination (bright fieldillumination) and a light of 750 nm or over in wavelength for dark fieldillumination.

FIGS. 33 and 34 respectively show further in detail the configuration ofthe optical system in the pattern inspection apparatus shown in FIGS. 31and 32. FIG. 33 is a plan view and FIG. 34 is a front view. In otherwords, an infinite compensation type objective lens 9 is used andtherefore a second objective lens (also referred to as tube lens) 303with a long focal distance (for example, f=200 nm) is required. Thelinear image sensor 12 a for annular-looped illumination (bright fieldillumination) and the linear image sensor 308 for dark fieldillumination are formed with a TDI (Time Delay & Integration) type imagesensor.

In this embodiment, a polarization beam splitter (PBS) 8 a′ and a λ/4plate (¼ wavelength plate) 51 are provided between the objective lens 9and a second objective lens 303. Since the lights remain parallelbetween the objective lens 9 and the second objective lens 303, anydeterioration such as aberration is not caused even though the aboveoptical elements 8 a′ and 51 are inserted. The functions of the PBS 8 a′and the λ/4 plate 51 are as shown in FIGS. 35 and 36. Of circularillumination light or annular-looped illumination light 330, Ppolarization light passes through the PBS 8 a′ and S polarization lightis reflected to reach the λ/4 plate 51. The S polarization light 332,which has reached the λ/4 plate 51 to include a component the phase ofwhich is delayed equivalent to 90 degrees (the refractive indexes of anextraordinary ray and an ordinary ray are unequal and the length of theoptical path of the extraordinary ray is longer than the latter.Therefore, a phase difference π/2 occurs between the extraordinary rayand the ordinary ray and the amplitudes of these rays are equal.), isconverted to circular polarization light or elliptical polarizationlight 334 and irradiated onto a wafer which is the inspected object 1through the objective lens 9.

The diffraction light (reflection light) entering into the pupil 10 a ofthe objective lens 9 reaches again the λ/4 plate 51 and the circularpolarization light or the elliptical polarization light becomes the Ppolarization light 333. This P polarization light 333 transmits throughthe PBS 8 a′ and the second objective lens 303 and reaches the imagesensor 12 a as the detector. FIG. 36 indicates that, when the angle ω tothe λ/4 wavelength plate 51 (angle formed by the linear polarizationplane of the incident light and the main cross section of the wavelengthplate 51) of the incident light (S polarization light) 332, which isconverted to the linear polarization light by the PBS 8 a′ , isaccurately 45° (+or−), the incident light 332 of linear polarization canbe converted to the circular polarization light 334 (or vice versa).When the angle ω is other than 45°, the linear polarization light isconverted to the elliptical polarization light 334 (or vice versa).

FIGS. 37 and 38 show the effects of this embodiment. The inspectedobject 1 is a pattern comprising lines and spaces of a 256 Mb DRAM (ahigh density grid pattern with pitch P of 0.61 μm). FIG. 37 shows thebrightness (detection intensity) of the pattern received by the imagesensor 12 a to the rotating direction of the above pattern. The circularpolarization annular-looped illumination (including ellipticpolarization annular-looped illumination) in FIG. 37 are based on theembodiments shown in FIGS. 31 to 34. The linear polarizationillumination in the diagram corresponds to the illumination having noλ/4 plate 51. The half mirror in the diagram indicates an illumination(illumination using the λ/4 plate 51) for which a typical half mirror isused instead of the PBS 8 a′.

From the relationship shown in FIG. 37, it is apparent that the imagesignals having high brightness (detection intensity) can be obtainedfrom the image sensor 12 a without being largely affected by thedirectionality of the pattern, by applying the circular polarizationannular-looped illumination (including the elliptical polarizationannular-looped illumination) even though a high density pattern on theinspected object 1 has various rotation angles as a memory cell patternas shown in FIG. 24. By using the annular-looped illumination, whetherlinear polarization illumination (S polarization illumination) or halfmirror illumination (using the λ/4 plate 51), the image signals havinghigher brightness (detection intensity) can be obtained from the patternformed on the inspected object 1 which has a peripheral circuit parthaving a special directionality as compared with application of the onlyordinary circular illumination.

It is apparent that the half mirror illumination (using the λ/4 plate51) is superior to the linear polarization illumination (S polarizationillumination). That the image signals having a high brightness(detection intensity) can be obtained from the image sensor 12 a asdescribed above means that highly efficient illumination for the highdensity pattern can be implemented.

FIG. 38 shows a contrast (a ratio of the minimum value to the maximumvalue indicating the resolution) from the pattern received by the imagesensor 12 a in the rotating direction of the pattern. In FIG. 38, thecircular polarization annular-looped illumination (including ellipticalpolarization annular-looped illumination) is based on the embodimentsshown in FIGS. 31 to 34. In the diagram, there is only circularpolarization illumination, and linear polarization illuminationcorresponds to S polarization illumination without the λ/4 plate 51.

In case of circular polarization annular-looped illumination, thecontrast to the angle of the pattern is not fixed because completecircular polarization is not obtained in the experiment and ellipticalpolarization appears. The ellipticity can be reduced to obtain a truecircle by entering a linear polarization incident light into an opticalelement (λ/4 plate 51) (the direction of electric vector oscillation isaligned in parallel with or normal to the incident plane) and circularpolarization is used by using the phase plate before entry into theinspected object 1.

From the relationship shown in FIG. 38, it is apparent that the imagesignals having a high contrast (high resolution) can be obtained fromthe image sensor 12 a without being largely affected by thedirectionality of the pattern, by applying the circular polarizationannular-looped illumination (including the elliptical polarizationannular-looped illumination) even though a high density pattern on theinspected object 1 has various rotation angles as a memory cell patternas shown in FIG. 24.

Those image signals having a high contrast can always be obtained fromthe image sensor 12 a without depending on the direction of the highdensity pattern, by simultaneously using circular polarizationillumination and annular-looped illumination and consequently micro finedefects on the high density pattern can be detected. The image signalshaving a high contrast (high resolution) can be obtained from simplecombination of normal circular illumination and circular polarizationillumination (only circular polarization illumination) without beinglargely affected by the directionality of the high density pattern fromthe image sensor 12 a as compared with the normal circular illumination.The image signals having a higher contrast (high resolution) than incase of only circular polarization illumination can be obtained bysimultaneously using the circular polarization illumination and theannular-looped illumination.

By using the annular-looped illumination, the image signals having thehigh contrast (high resolution) can be obtained from a high densitypattern which is formed on the inspected object 1 and has a specialdirectionality as the peripheral circuit part even with the linearpolarization illumination (S polarization illumination). However, Incases of general super LSIs (VLSI and ULSI) on which high densitypatterns are provided and therefore it is difficult to irradiate thelinear polarization light to these patterns at all times in accordancewith the directions of high density patterns. If the patterns have aspecified directionality as a specified wiring pattern, it is necessaryto control the polarization in the linear polarization illumination tobe aligned with the direction of the wiring pattern and to limit thelinear polarization illumination only to the specified wiring pattern.In doing so, the image signals having the high contrast can be detectedfrom the image sensor 12 a.

Though the PBS 8 a′ is used in the description of the above embodiments,similar effects can be obtained by using the half mirror which is coatedwith a dielectric multi-layer film. A polarization plate can be used toobtain the linear polarization illumination instead of the PBS 8 a′. Inthis case, the quantity of light passing through the polarization plateis attenuated and the brightness (detection intensity) is decreased butthe contrast is improved as in case of the PBS 8 a′.

In a seventh embodiment of the present invention, a diffusion plate fordiffusing light is inserted into the position (position in conjunctionwith the pupil 10 a of the objective lens 9) of the field diaphragm 319or the filter (opening diaphragm) 5 for annular-looped illumination.This diffusion plate is specified with the sand No. 800. Such diffusionplate serves to increase a diffusibility of the illumination light inirradiation of only the annular-looped illumination light orsimultaneous irradiation of the polarized illumination and theannular-looped illumination to the inspected object 1, and a bright anduniform reflection light can be obtained in spite of the variation ofthe surface of metallic wiring pattern, such as fine recesses andprojections and therefore the surface of the metallic wiring pattern canbe detected or observed as the image having uniform brightness by theimage sensor 12 a or the TV camera TV₁ for bright field observationthrough the objective lens 9.

This diffusion illumination is not compatible with annular-loopedillumination and polarization illumination and can be simultaneouslyimplemented in the same optical system. The extent of diffusion isselected in accordance with the pattern on the inspected object 1.

In the embodiments shown in FIGS. 31 to 34, the image sensor 12 a isformed with the TDI (Time Delay & Integration) type image sensor and, ifthe reflectivity of the pattern of the inspected object 1 is low and thebrightness (detection intensity) is insufficient, the image sensor canbe controlled to increase its accumulation time. Thus, the accumulationtime of the image sensor can be appropriately determined in accordancewith the pattern of the inspected object 1. Furthermore, theaccumulation time of the image sensor can be determined according to theilluminating conditions for the pattern of the inspected object 1.

The following describes analyses of the causes of defects, for examplein semiconductor manufacturing processes as shown in an eighthembodiment of the present invention as illustrated in FIG. 39, byentering defect determination output 18 to be outputted from thecomparator circuit 17 of the apparatus shown in FIG. 1 and defectinformation 40 to be outputted from the CPU 20, and production of highquality semiconductor chips at a high yield by eliminating the analyzedcauses of defects.

As shown in FIG. 39, there is provided a semiconductor manufacturingline 380 with a conveying path 381 for a semiconductor wafer 1 a. A CVDunit 382 is provided for executing a CVD film forming step for formingan insulation film and a sputtering unit 383 is provided for executing asputtering step for forming a wiring film of the semiconductor steps. Anexposure unit 384 is provided for executing exposure steps forapplication of resist, exposure and development of the semiconductormanufacturing steps and an etching unit 385 is provided for executing anetching step for patterning of the semiconductor manufacturing steps.Thus, semiconductor wafers are manufactured through variousmanufacturing steps.

A computer 390 is provided for analyzing the causes of defects orfactors of defects in the manufacturing line 380 comprising the processunits 382, 383, 384 and 385 for manufacturing the above-describedsemiconductors by entering defect determination output 18 outputted fromthe comparator circuit 17 and defect information 40 outputted from theCPU 20 shown in FIG. 1. The computer 390 for analysis comprises aninterface 391 for entering the defect determination output 18 outputtedfrom a comparator circuit 17 and the defect information 40 outputtedfrom the CPU 20 shown in FIG. 1; a CPU 392 for executing processing suchas analysis; a memory 393 which stores programs such as for analysis;control circuits 394, 395, 396 and 397; an output unit 398 such as aprinting unit for outputting the results of analysis such as causes ofdefects; a display unit 399 for displaying various data; an input unit(comprising a keyboard, a disc and others) 401 for entering data relatedto, for example, process units 382, 383, 384 and 385 which cannot beobtained from the units shown in FIG. 1 and data related to thesemiconductor wafer 1 a to be supplied to the manufacturing line 380; anexternal storage unit 402 which stores history data of correlationbetween defects which occur on the semiconductor wafer 1 a and thecauses of defects or the factors of defects due to which a defect iscaused in the manufacturing line 380 which comprises process units 382,383, 384 and 385, or a data base; an interface 403 for supplyinginformation 410 related to the causes of defects or the factors ofdefects analyzed by the CPU 392 to the process units 382, 383, 384 and385; and a bus line 400 for connecting these component units.

The CPU 392 in the computer 390 for analysis analyzes the causes ofdefects or the factors of defects due to which a defect is caused in themanufacturing line 380 which comprises process units 382, 383, 384 and385 according to the defect determination output 18 and the defectinformation 40, and the history data of correlation between defects onthe semiconductor wafer 1 a and the causes of defects or the factors ofdefects in the manufacturing line 380 or a data base, which are storedin the external storage unit 402, and supplies the information 410related to the analyzed cause or factor of defect to the process units382, 383, 384 and 385.

The process units 382, 383, 384 and 385 to which the information 410related to the causes of defects or the factors of defects is suppliedcan feed a satisfactory semiconductor wafer 1 a to a following processby controlling various process conditions including cleaning, and byeliminating the causes of defects or the factors of defects andconsequently manufacture semiconductors at a high yield. Thesemiconductor wafer 1 a, a defect of which is inspected by the apparatusshown in FIG. 1, is sampled in a unit of the semiconductor wafer 1 a ora lot thereof in the front and rear processes where the defect is liableto be caused in the manufacturing line 380.

The CPU 392 in the computer 390 for analysis analyzes the causes ofimpurities or the factors of impurities due to which an impurity iscaused in the manufacturing line 380 according to impurity informationobtained from and entered by the CPU 20 in accordance with an impuritysignal detected by an image sensor 308, and the history data ofcorrelation between the impurities on the semiconductor wafer 1 a andthe causes of impurities or the factors of impurities due to which animpurity is formed in the manufacturing line 380 or a data base, whichare stored in the external storage unit 402, and supplies theinformation 410 related to the analyzed cause or factor of impurity tothe process units 382, 383, 384 and 385.

The process units 382, 383, 384 and 385 to which the information 410related to the causes of impurities or the factors of impurities issupplied can feed a defect-free semiconductor wafer 1 a to a followingprocess by controlling various process conditions including cleaning,and by eliminating the causes of impurities or the factors of impuritiesand consequently manufacture semiconductors at a high yield.

The present invention enables inspection with high reliability of microfine defects which occur on micro fine patterns formed on asemiconductor substrate having micro fine patterns such as asemiconductor wafer, a TFT substrate, a thin film multi-layer substrateand a printed board, and to manufacture semiconductor substrates at ahigh yield by feeding back the results of inspection to themanufacturing processes for semiconductor substrates. In addition, thepresent invention is adapted to detect defects on micro fine patterns bydetecting high resolution image signals from micro fine patterns on theinspected object with annular-looped illumination applied thereto,comparing these high resolution image signals with the reference highresolution image signals and erasing micro fine patterns according toconsistency of these image signals to detect the defects on the microfine patterns and therefore, provides an effect to inspect the defectson micro fine patterns in high reliability.

The present invention is adapted to irradiate the annular-loopedillumination onto micro fine patterns on the inspected object, attenuateat least part of the 0th order diffraction light of the 0th orderdiffraction light and the first order diffraction light (+ first orderdiffraction light or − first order diffraction light), which areproduced from the micro fine pattern and entered into the pupil of theobjective lens, by the filter for controlling the light quantity whichis provided at a position in conjunction with the pupil of the objectivelens, receive the 0th order diffraction light and the first orderdiffraction light, detect image signals of high resolution from themicro fine pattern, compare the high resolution image signals with thereference high resolution image signals, erase the micro fine patternaccording to consistency of these image signals, and detect the defectson the micro fine pattern, and therefore provides an effect to inspectthe defects on micro fine patterns in high reliability. Further, thepresent invention enables detection of the images or image signals fromthe micro fine patterns in a high resolution (resolution power) and alarge difference of shade (brightness), by simultaneously using theannular-looped illumination and the polarization illumination(particularly, circular or elliptic polarization illumination isexcellent) for micro fine patterns on the inspected object. The presentinvention provides an effect enabling to detect the images or imagesignals from the micro fine patterns having various directionalities ina high resolution (resolution power) and a large difference of shade(brightness), by simultaneously using the annular-looped illuminationand the polarization illumination (particularly, circular or ellipticpolarization illumination is excellent) for micro fine patterns havingvarious directionalities on the inspected object.

The present invention is adapted to detect the image signals having ahigh resolution (resolution power) and a large difference of shade(brightness) from the micro fine patterns having variousdirectionalities on the inspected object by simultaneously using theannular-looped illumination and the polarization illumination(particularly, circular or elliptic polarization illumination isexcellent) for micro fine patterns, compare these image signals with thereference image signals having a high resolution (resolution power) anda large difference of shade (brightness), erase the micro fine patternshaving various directionalities according to consistency of these imagesignals, to detect the defects on the micro fine patterns having variousdirectionalities, and therefore provides an effect of inspecting thedefects of micro fine patterns having various directionalities in highreliability.

The present invention enables detection of images or image signals witha high resolution (resolution power) adapted to a micro fine pattern bydetecting an image based on a diffraction light which is produced from amicro fine pattern on the inspected object and entered into the pupil ofthe objective lens, controlling the annular-looped illumination (forexample, OUT σ and IN σ) according to this image, and applying thiscontrolled annular-looped illumination to the micro fine pattern on theinspected object. Further, the present invention is adapted to detectthe defects on the micro fine pattern by detecting an image based on adiffraction light which is produced from a micro fine pattern on theinspected object and entered into the pupil of the objective lens,controlling the annular-looped illumination (for example, OUT σ and INσ) according to this image, applying this controlled annular-loopedillumination to the micro fine pattern on the inspected object to detectthe image signals of a high resolution (resolution power) adapted to amicro fine pattern, comparing these image signals having a highresolution with the reference image signals having a high resolution,and erasing the micro fine pattern according to consistency of theseimage signals to detect the defects on the micro fine pattern andtherefore provides an effect enabling to inspect the defects on themicro fine pattern in high reliability.

Additionally, the present invention enables detection of images or imagesignals with a high resolution (resolution power) adapted to a microfine pattern by identifying (observing or detecting) a localitydistribution of the 0th order diffraction light and the first orderdiffraction light (+ first order or − first order diffraction light)which are produced from a micro fine pattern on the inspected object andentered into the pupil of the objective lens, controlling theannular-looped illumination (for example, OUT σ and IN σ) according tothis identified (observed or detected) locality distribution of thediffraction light, and applying this controlled annular-loopedillumination to the micro fine pattern on the inspected object.

The present invention is adapted to identify (observe or detect) alocality distribution of the 0th order diffraction light and the firstorder diffraction light (+ first order or − first order diffractionlight) which are produced from a micro fine pattern on the inspectedobject and entered into the pupil of the objective lens, control theannular-looped illumination (for example, OUT σ and IN σ) according tothis identified (observed or detected) locality distribution of thediffraction light, apply this controlled annular-looped illumination tothe micro fine pattern on the inspected object to detect image signalsof a high resolution (resolution power) adapted to the micro finepattern, compare this high resolution image signal with the referencehigh resolution image signal, and erase the micro fine pattern accordingto consistency of these image signals to detect the defects on the microfine pattern and therefore provides an effect enabling to inspect thedefects on the micro fine patterns in high reliability.

Further, the present invention is adapted to detect image signals with ahigh resolution (resolution power) adapted to a micro fine pattern bydetecting an image showing a density of the micro fine pattern based onthe diffraction light which is produced from the micro fine pattern onthe inspected object and entered into the pupil of the objective lens,controlling the annular-looped illumination (for example, OUT σ and INσ) according to this image, and applying this controlled annular-loopedillumination to the micro fine pattern on the inspected object, and bycomparing this high resolution image signal with the reference highresolution image signal and erasing the micro fine pattern according toconsistency of these image signals to detect the defects on the microfine pattern and therefore provides an effect enabling to inspect thedefects on the micro fine patterns in high reliability.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What is claimed is:
 1. A method of detecting an object to be inspected,comprising the steps of: illuminating the object with a light having apredetermined range of wavelength emitted from a light source andpassing through an objective lens; detecting an image of the objectilluminated by the light through the objective lens using a time delayintegration sensor; outputting an output signal of the detected imagefrom the time delay integration sensor; and processing the output signalfrom the time delay integration sensor for obtaining informationrelating to the object, using a variable defect detection sensitivitywhich varies according to the density of the pattern to be inspectedduring the processing.
 2. A method according to claim 1, wherein therange of wavelength of the light extends from 400-600 nm.
 3. A methodaccording to claim 1, wherein a source of the light is a Xenon lamp. 4.A method according to claim 1, wherein the light illuminating the objectis an incoherent light.
 5. A method according to claim 1, wherein thelight illuminating the object is a coherent light.
 6. A method accordingto claim 1, wherein said information relates to a defect of a patternformed on the object.
 7. A method according to claim 1, wherein saidtime delay integration sensor has a construction such that a pluralityof one-dimensional image sensors functioning as a pattern detector arearranged in a two-dimensional form, and an output of a precedingone-dimensional image sensor for imaging a certain position of onepattern is delayed for a predetermined time period, and an output of asucceeding one-dimensional image sensor adjoining said precedingone-dimensional image sensor, also images the same position of the samepattern as said preceding one-dimensional image sensor and issequentially added to the delayed output of said precedingone-dimensional image sensor to derive a summation output.
 8. Anapparatus for detecting information relating to a pattern on an objectto be inspected, comprising: an illuminator having a light source whichemits a light having a predetermined range of wavelength, and anobjective lens through which the light passes and illuminates an object;an image sensor which detects an image of the object through theobjective lens using a time delay integration sensor, and which outputsa signal of the detected image; and a processor which processes theoutput signal from the image sensor and obtains an information relatingto the object, using a variable defect detection sensitivity whichvaries according to the density of the pattern to be inspected duringthe process by the processor.
 9. An apparatus according to claim 8,wherein the range of wavelength of the light extends from 400-600 nm.10. An apparatus according to claim 8, wherein the light source is aXenon lamp.
 11. An apparatus according to claim 8, wherein the lightilluminating the object is an incoherent light.
 12. An apparatusaccording to claim 8, wherein the light illuminating the object is acoherent light.
 13. An apparatus according to claim 8, wherein theinformation obtained by the processor relates to a defect of a patternformed on the object.
 14. An apparatus according to claim 8, whereinsaid time delay integration sensor has a construction such that aplurality of one-dimensional image sensors functioning as a patterndetector are arranged in a two-dimensional form, and an output of apreceding one-dimensional image sensor for imaging a certain position ofone pattern is delayed for a predetermined time period, and an output ofa succeeding one-dimensional image sensor adjoining said precedingone-dimensional image sensor also images the same position of the samepattern as said preceding one-dimensional image sensor and issequentially added to the delayed output of said precedingone-dimensional image sensor to derive a summation output.
 15. A methodof inspecting a patterned wafer, comprising the steps of: illuminating alight having a predetermined range of wavelength onto a pattern on thewafer; detecting an image of the pattern using a time delay integrationsensor; outputting an output signal from the time delay integrationsensor corresponding to the detected image; and processing the outputsignal from the time delay integration sensor for obtaining informationrelating to the pattern, using a variable defect detection sensitivity,which varies according to the density of the pattern to be inspectedduring the processing.
 16. A method according to claim 15, wherein saidvariable defect detection sensitivity varies according to a position onthe wafer.
 17. A method according to claim 15, wherein said variabledefect detection sensitivity varies according to the pattern beinginspected.
 18. A method according to claim 15, wherein said variabledefect detection sensitivity changes by varying a threshold value todetect a defect.
 19. A method according to claim 15, wherein the lightis emitted from a Xenon lamp.
 20. A method according to claim 15,wherein the output signal from the time delay integration sensorprovides information relating to a defect of the pattern.
 21. A methodaccording to claim 15, wherein said time delay integration sensor has aconstruction such that a plurality of one-dimensional image sensorfunctioning as a pattern detector are arranged in a two-dimensionalform, and an output of a preceding one-dimensional image sensor forimaging a certain position of one pattern is delayed for a predeterminedtime period, and an output of a succeeding one-dimensional image sensoradjoining said preceding one-dimensional image sensor also images thesame position of the same pattern as said preceding one-dimensionalimage sensor and is sequentially added to the delayed output of saidpreceding one-dimensional image sensor to derive a summation output. 22.An apparatus for inspecting a patterned wafer, comprising: a lightsource which focuses and irradiates an illumination light onto a patternon the wafer; a time delay integration sensor which receives an image ofthe pattern of the wafer and which outputs an output signalcorresponding to the received image; and a processor which processes theoutput signal from the time delay integration sensor and obtains aninformation relating to the pattern using a variable defect detectionsensitivity, which varies according to the density of the pattern to beinspected during the process by the processor.
 23. An apparatusaccording to claim 22, wherein said variable defect detectionsensitivity varies according to a position on the wafer.
 24. Anapparatus according to claim 22, wherein said variable defect detectionsensitivity varies according to the pattern being inspected.
 25. Anapparatus according to claim 22, wherein said variable defect detectionsensitivity changes by varying a threshold value to detect a defect. 26.An apparatus according to claim 22, wherein the light is emitted from aXenon lamp.
 27. An apparatus according to claim 22, wherein the outputsignal from the time delay integration sensor provides informationrelating to a defect of the pattern.
 28. An apparatus according to claim22, wherein said time delay integration sensor has a construction suchthat a plurality of one-dimensional image sensors functioning as apattern detector are arranged in a two-dimensional form, and an outputof a preceding one-dimensional image sensor for imaging a certainposition of one pattern is delayed for a predetermined time period, andan output of a succeeding one-dimensional image sensor adjoining saidpreceding one-dimensional image sensor also images the same position ofthe same pattern as said preceding one-dimensional image sensor and issequentially added to and the delayed output of said precedingone-dimensional image sensor to derive summation output.